Raducanu forced to retire trailing 4-6, 6-3, 3-0
Briton had started well and won the opening set
She was unable to complete match due to glute issue
Ostapenko will now play Alexandrova in the final
Raducanu moves from 77th to 66th in world rankings
Emma Raducanu was facing more questions over her fitness after retiring for the fifth time in her professional career in the semi-finals of the Korea Open.
Forced off with a glute problem as she trailed 4-6, 6-3, 3-0 to Latvian Jelena Ostapenko, it was her ninth tournament hampered by injury since her breakthrough last year.
The latest fitness worry is all the more frustrating for 19-year-old Raducanu, given she had been showing glimpses of her best in Seoul after dismal results in recent months.
Since retiring at Wimbledon last year in the fourth round with breathing difficulties and sickness, Raducanu has quit her first round at Abierto Zapopan with a leg injury, the Italian Open with a back injury and then the Nottingham Open with a problem on her left side.
There have also been persistent blister issues hampering her efforts to live up to the heavy weight of expectation since winning the US Open last year.
She had been bidding to reach her first final in a regular WTA Tour event in Korea, and had come from a break down to win the first set, but former French Open champion Ostapenko levelled in the second and then edged ahead. She fell behind early in the first set but broke back immediately and claimed a decisive break at 4-4.
Raducanu carried the momentum into the second set and broke again but this time Ostapenko hit back quickly. She needed a medical time-out and could not halt Ostapenko's charge when she returned to the court.
Ostapenko, who broke again and went on to take the second set before taking control of the third, goes through to play Ekaterina Alexandrova in the final after the second seed's 6-2, 6-4 victory over Tatjana Maria.
Raducanu moves from 77th to 66th in the world rankings after her encouraging tournament, but a fifth retirement in 15 months will be a significant concern for her team. Her play in recent weeks had been reminiscent of her composed hitting during her fairytale US Open run.
Emma Raducanu vs Jelena Ostapenko: as it happened
... following her participation in Korea Open, will go from 77th to 66th.
This is Raducanu's fourth retirement
In fifteen months. Quite a stark figure.
Hopefully, this injury won't be a long-term setback - her post-US Open intentions were to take part in smaller WTA tour events, like the Slovenia and Korea Opens, for the remainder of the season.
Her play in Korea was certainly reminiscent of her composed hitting in her fairytale US Open run, and both she and her coach, Dmitry Tursunov, will hope to build on reaching this semi-final.
That being said
Ostapenko's performance was laudable. Her control of the power shift, following the timeout, as well as some impressive hitting and choice winners, made her a more-than worthy finalist today.
Ostapenko will play Ekaterina Alexandrova in tomorrow's final.
A huge disappointment for Raducanu
After the first set, Raducanu looked composed and confident, and had her form continued, could have seen off the No 1 seed. But as has happened so often over the past year, injury trouble intervened.
Having been hampered by blisters, side strain, and hip and back issues previously, Raducanu has retired from a number of matches in the year since her 2021 US Open win. Her week in Korea was viewed with a lot of optimism, making this retirement all the more poignant.
RADUCANU RETIRES: Ostapenko wins 4-6, 6-3, 3-0
Ostapenko's touch is heaven-sent in the opening moments of the set, with another forehand winner striking the sideline, unplayable. She streaks to love-40, looking comfortable. Momentum sits with her, and Raducanu, who has started to look slow, falls quickly, with Ostapenko taking the double break at pace.
After the game wraps up, Raducanu goes to shake Ostapenko's hand: she concedes the semi-final.
Raducanu* 6-4, 3-6, 0-2 Ostapenko (*denotes next server)
Raducanu can only hit long off Ostapenko's strong serve, then into the net, to put the Latvian 30-love ahead. With a low backhand, Ostapenko clears the net to set up a clean passing shot, and shortly after, takes what must be the quickest game of the match.
Third set: Raducanu 6-4, 3-6, 0-1 Ostapenko* (*denotes next server)
Raducanu takes first blood in the third and final set after Ostapenko, backed into a corner, hits her cross-court return long and out of play. Her forehand in the ensuing rally, however, glances just out at the wrong angle, levelling the players 15-all.
Ostapenko gets an extraordinary stroke of luck, smacking the net cord for the shot to bounce over a sprinting Raducanu to go in behind her. With an ace, Raducanu draws them level again, but Ostapenko plays a deep forehand groundstroke which bypasses Raducanu on the baseline to set her up with break point.
She breaks quickly, setting out her intentions.
End of second set: Raducanu 6-4, 3-6 Ostapenko
Serving for the set, Ostapenko opens with a double fault, and remonstrates herself on court. A good return from Raducanu, moving well for now, sees Ostapenko make an error into the net, putting her love-30 behind.
But Ostapenko has Raducanu on the run, sending her this way and that on the baseline, before hitting a backhand down the line which Raducanu can't get to in time. She levels with an ace for 30-all, and goes ahead when Raducanu's forehand lands in the net.
At set point, Raducanu hits a commanding forehand return which flies past off-guard Ostapenko, bringing them to deuce. But with an ace, and impressive serve on her advantage, Ostapenko takes the set.
We go to a third in Seoul.
Raducanu 6-4, 3-5 Ostapenko* (*denotes next server)
Raducanu has just won one point since her timeout, to Ostapenko's nine, and will have to pull off an almighty mentality shift after again being seen by the physio during the break.
Ostapenko hits long in her opening return, but hits a springy winner past Raducanu to level them, 15-all. The No 1 seed overpowers her cross-court return, under pressure from a strong Raducanu serve, and Raducanu looks much brighter on the following rally, pinning Ostapenko to the baseline until she finds the net, 40-15.
Raducanu double faults, eroding her lead, but holds with a strong backhand which a misdirected Ostapenko cannot reach.
Raducanu* 6-4, 2-5 Ostapenko (*denotes next server)
Moving up the court, Raducanu is bypassed by Ostapenko's fluid backhand, and on her next return, Raducanu finds in the net to fall 30-love behind.
With an ace, Ostapenko reaches 40-0, zipping through her games, transformed since the first set, and holds comfortably when a high dropshot of Raducanu's falls just before the net.
Raducanu 6-4, 2-4 Ostapenko* (*denotes next server)
A strong return from Ostapenko sees Raducanu bundle her response into the net, but she glitters in the next rally, picking up a fast-moving forehand to play her own to the back corner of the court where it bypasses Ostapenko, 15-all.
Ostapenko plays a towering backhand to the back of the court, which Raducanu cannot catch, and when she repeats the shot, again off Raducanu's second serve, Raducanu plays her response out, 15-40.
She wraps up her break with another unplayable forehand, taking advantage of a possible shift in momentum after the timeout.
Raducanu returns to court
Treatment complete, she's due to head out and straight onto serve.
Medical timeout for Raducanu
During the break, Raducanu's physio comes onto court and looks to be stretching out her lower back. It would be so disappointing for Raducanu, whose year has been defined by small injuries, to have something impact her match now.
She takes a medical timeout for an issue with her left glute, and heads off court.
Raducanu* 6-4, 2-3 Ostapenko (*denotes next server)
Ostapenko, on the attack, serves up an ace, and then beats Raducanu in the rally with a cleanly-hit backhand which again is perfectly placed. Another ace takes her to 40-0 at warp speed, and with a second serve ace, she holds quickly and confidently.
Raducanu 6-4, 2-2 Ostapenko* (*denotes next server)
Ostapenko is up for the fightback, and after Raducanu hits long, Ostapenko completes a blinding rally with a well-angled cross-court dropshot which her opponent runs for, but cannot reach.
She reaches love-40 after Raducanu falters on her backhand, but Ostapenko has her own faulty backhand with a glancing return which flies out past the sidelines, gifting Raducanu a way in to stop the quick break back.
Raducanu's strong serve is clumsily returned, and she can spring forward to smack a backhand cross-court, 30-40. But with an on-the-line, unplayable shot, Ostapenko gets her break.
Raducanu* 6-4, 2-1 Ostapenko (*denotes next server)
Double fault from Ostapenko, and Raducanu steps up with aggression to pick off her second serve with a dominant return, forcing Ostapenko into an error and fall love-30 behind. Raducanu's springing backhand dropshot goes just wide into the tramlines, allowing Ostapenko into the game, but when she nets again, Raducanu gets two break points quickly.
Ostapenko unleashes her dangerous forehand, catching Raducanu on the back foot, and the shot goes leaping past her to shave off one of the break points, but an advancing Raducanu moves up the court to play an unreturnable backhand and complete her break.
Raducanu 6-4, 1-1 Ostapenko* (*denotes next server)
Raducanu opens with an unplayable serve, then brings down an airy shot of Ostapenko's with a whipcracking volley which springs in before the baseline. Another powerful baseline forehand from Ostapenko brings her in at 30-15, with a clean passing shot.
But Raducanu's service game has given her the upper hand today, and with a final indomitable serve she takes her hold at pace.
Second set: Raducanu* 6-4, 0-1 Ostapenko (*denotes next server)
Two strong serves get Ostapenko off the mark in the second set as she lays out her intention after falling behind. But Raducanu makes it 30-15 after directing Ostapenko to the back corner of the court, where she plays squarely into the tramlines.
With a lovely cross-court backhand, Raducanu angles the ball perfectly to whip past Ostapenko on the baseline, 30-all. From deuce, Ostapenko gets the first advantage with a well-placed backhand which lands just on the line, and after a reset, a sensational second following a comprehensive forehand display which ends with the No 1 seed tucking the ball in the corner to elude her opponent.
Ostapenko completes her first hold handily.
This has grown into quite the match-up
From a break down, Raducanu put in a commanding shift in the first set, against an opponent who has not given her much leeway.
Momentum is firmly with the British No 2 now, who will look to continue in her tournament form, having not dropped a set so far in Seoul.
End of first set: Raducanu 6-4 Ostapenko
Raducanu confidently pulls down a high, aerial, return from Ostapenko to play into a dominant rally, as she forces Ostapenko to play into the tramlines. With an ace, she goes 30-love up. But Ostapenko has some terrific returns in her arsenal, and plays a straight-down-the-line forehand which evades the Briton.
Raducanu gets two set points after pushing Ostapenko backwards, where she powers into the net from the baseline. Ostapenko has responses, however, and she reaches deuces following a well-angled backhand cross-court rally which ends with a winner.
With an unplayable serve, Raducanu gets the first advantage, and that's all she needs: another strong second serve hands Raducanu the opening set.
Raducanu* 5-4 Ostapenko (*denotes next server)
A reached-for shot from Raducanu is feasted upon by Ostapenko, who can set up a squarely-hit shot which bypassing Raducanu on the baseline.
Raducanu goes ahead with an eye-popping forehand which lands just on the sideline, 30-15, then reaches break point after Ostapenko plays an error into the net. Ostapenko can reduce the deficit, but when she double faults, Raducanu takes the break to move ahead, and try for the set on her serve.
Raducanu 4-4 Ostapenko* (*denotes next server)
Raducanu nets then plays a double fault, quickly under pressure in the opening moments of her service. Directing Ostapenko around the baseline, she gets into the points 15-30 when the Latvian plays short into the net.
Growing into the game, she reaches 40-30 with a lovely backhand which takes advantage of Ostapenko's weak, running return, to play just past her at the back of the court. Ostapenko keeps up the pressure in the next rally, pushing the players to deuce, but with a bright combination of forehand and backhand shots at mid-court, Raducanu takes her advantage and holds her serve.
Raducanu* 3-4 Ostapenko (*denotes next server)
Ostapenko's holds have come at a greater price today, and Raducanu takes the opening point on her opponent's serve. Ostapenko gets into the points when Raducanu springs forward to the net, going for a backhand slice volley but punching the shot into the net.
This time, however, Ostapenko can be more dominant, and at 40-15 cannot be caught by Raducanu, who grapples with a strong serve to fire the ball way out of play cross-court.
Raducanu 3-3 Ostapenko* (*denotes next server)
Raducanu's second serve bullies Ostapenko into a too-strong response which goes long, and the second time, the same serve has Ostapenko hitting wildly out to the crowd.
Dangerous on serve, Raducanu skates to 40-love, but Ostapenko plays her way into the game with a controlled and springy forehand aimed perfectly for the corner by the baseline.
Raducanu is business-like as she wraps up her serve, however, completing another speedy hold.
Raducanu* 2-3 Ostapenko (*denotes next server)
Raducanu manages a return off a strong first serve from Ostapenko, then another, but Ostapenko on the front-foot overpowers her. More directional on the second point, Raducanu gets into the game after pinning Ostapenko to the back corner, where her backhand goes into the net.
But Ostapenko's passing shots have been of excellent quality, and she plays another to make 30-15 that lands deep in the back corner of the court. Raducanu has no hope of returning the shot.
Raducanu gets to deuce from 40-15 behind, with a squarely-hit backhand straight down the sideline to bypass Ostapenko. Defending against Ostapenko's opening advantage, she puts her opponent under pressure to find the net, resetting the players.
But on the second time of asking, Ostapenko takes her advantage to hold the game, with a well-placed forehand.
Raducanu 2-2 Ostapenko* (*denotes next server)
Ostapenko wins another challenge, the ball landing in by a whisker after a blazing cross-court rally to open up Raducanu service game. Raducanu levels with an ace, and playing another to reach 40-15 at pace.
Forced to sprint across the baseline to pick up Ostapenko's well-placed backhand, Raducanu nets. But she takes the game with a competent hold, her clean, strong, hitting looking composed in the face of Ostapenko's power.
Raducanu* 1-2 Ostapenko (*denotes next server)
Drawing her left, then right, Ostapenko plays a loaded shot which glances past Raducanu. Ostapenko quickly serves up an ace, looking to underscore her dominant play in the match so far.
But Ostapenko is by no means playing her finest so far, and when she plays a backhand into the net, Raducanu gets a way into the game, 30-40. A double fault, Ostapenko's first, sets up deuce. Playing a nifty ace, which looked out initially, but as Hawkeye shows by the finest of margins, it isn't.
But Raducanu gets one advantage, then another, going for the break. With a powerful cross-court backhand, she plays intimidatingly past the No 1 seed and completes the break back.
Raducanu 0-2 Ostapenko* (*denotes next server)
Raducanu holds Ostapenko up with a determined backhand rally, and Ostapenko plays out of the court to put Raducanu ahead, but she squanders an excellent opportunity of Ostapenko's weak return to play a passing shot which jumps just long to level them.
After serving a double fault, and finding the net under the thumb of Ostapenko, Raducanu looks to set up her opponent's first break.
Ostapenko takes the break after Raducanu finds the net, and Raducanu will try and force an immediate response.
First set: Raducanu* 0-1 Ostapenko (*denotes next server)
Ostapenko falters on her opening serve, and Raducanu can capitalise on a weaker second serve, forcing Ostapenko to hit long to win the opening point. Her next serve is stronger, however, and Raducanu can only net her return.
A strong forehand from Raducanu after a shaky first return puts Ostapenko in the net, going for a low shot at an angle. The Latvian is struggling to get her first serve away, but there's enough power in her second to pressure Raducanu just out on the tramline to level things, 30-30.
Ostapenko plays a fiery backhand passing shot, 40-30, but overhitting takes the players to deuce. Raducanu doesn't let Ostapenko take the game easily, and the players go to deuce five times, but a powerful serve and big, directional hitting edges it to give her the first hold.
Here come the players
Ostapenko and Raducanu emerge to cheers and applause from the crowd.
Raducanu swipes at the air with a racquet during the toss, which Ostapenko wins. She will opening the match serving.
Alexandrova books her place in the final
The Russian put in a comprehensive performance against Maria, winning the final game on serve to love in her 6-2, 6-4 victory.
But who will she face tomorrow? Raducanu and Ostapenko should be out on court in the next few minutes.
End of an era
Elsewhere in the tennis world, last night saw the final match of Roger Federer's career ahead of his retirement, and there were no shortage of emotions at the O2 Arena.
Read Simon Briggs' full report here.
In the first of today's semi-finals
Ekaterina Alexandrova has had a confident start against Tatjana Maria, winning the first set 6-2, and is 5-4 ahead in the second.
They're currently on Centre Court in Seoul, which means Raducanu's start will be a little delayed.
Welcome to our live coverage of Emma Raducanu vs Jelena Ostapenko in the Korea Open semi-finals.
Raducanu has won three games in succession for the first time since her stunning US Open win last year - but will have to overcome the top seed to reach her first final since that unforgettable Flushing Meadows triumph.
Raducanu is yet to drop a set in Seoul so far and played her best match to defeat third seed Magda Linette 6-2 6-2 last time out. And the British teenager is taking it all in her stride, describing her run as "pretty cool" ahead of the last-four clash.
The British No 2, who beat Japan's Moyuka Uchijima and Belgium's Yanina Wickmayer earlier this week, has rediscovered some of her best form since her US Open defence fell at the first hurdle.
Raducanu has slipped to 77th in the world rankings from a career-high of 10th but could return to the top 50 if she can win this title.
However, beating Ostapenko - the 2017 French Open champion - will be no easy task. The Latvian top seed was equally dominant in her own quarter-final victory over Victoria Jimenez Kasintseva.
But even if she does not progress to the final, Telegraph Sport's tennis correspondent believes Raducanu's improvement at this tournament offers promising signs for the future.
He writes: "Playing in this relative tennis backwater, Raducanu has finally gathered some momentum by collecting three victories on the bounce. Which, again, is something she hasn't managed since receiving that $2.5m cheque in New York 54 weeks ago.
"Taken in isolation, none of her three wins in Seoul looks like a game-changer. But together they suggest that Raducanu's confidence is gradually picking up after what has been an extremely testing year."
The players are due on court at 7.20am and we will have game-by-game updates for you throughout plus all the post-match reaction.