Novak Djokovic remained on course for a record-equalling sixth ATP Tour Finals title after a 7-6 (7/5), 7-6 (8/6) win over Taylor Fritz in Turin on Saturday.
Djokovic brushed off his bruising encounter with Daniil Medvedev the day before to boss the semi-final against the ninth-seeded American.
The 35-year-old Serb will face the winner of the second semi-final between Andrey Rublev and Casper Ruud.
Victory in Sunday's final will see him equal Roger Federer's haul of six wins in the tournament comprising the top eight players in the world this season.
"I had to fight to survive," said Djokovic, who has now reached the final of the season-ending event eight times and last won in 2015.
"I didn't feel very reactive or very comfortable. I knew coming into today's match from yesterday's gruelling battle against Medvedev, it would take me some time to adjust and find the dynamic movement I need against Fritz, who is one of the best servers on the Tour."
Djokovic has now beaten 25-year-old Fritz, in all six of their meetings.
"I'm extremely upset about the match, more so about the things that happen in a match that I can't control," said the American, who was playing for the first time in the Masters tournament having taken advantage of the withdrawal of world number one Carlos Alcaraz.
"But I'm sure in two weeks from now I'll look back and I'll say, yeah, like it was a really great week.
"Not only did I get the chance to play the World Tour Finals, I made it out of the group, had two good wins.
"I think my takeaways are that when Novak has played, he's been the best player.
"There's no doubt about that. When he hasn't played, which is a lot of the year, we've seen a lot of different results because when you take him out of the equation, I think everybody else playing is extremely close in level.
"There's 15 to 20 people that can all beat each other on any given day given the circumstances. That's the reason for a lot of these different results, different people winning. It's just how it happens."
Djokovic will aim for his second major title of the year, after Wimbledon, having missed a significant part of the season, including the Australian Open and the US Open, for his refusal to take the covid vaccine.
The Serb held on largely thanks to the efficiency of his serve -- he won 85 percent of the points played on his first serve in the first set and 75 percent throughout the match, and his ability to deliver the fatal blow at the right time.
Fritz did not make many mistakes, but they were all heavily penalised.
Djokovic is chasing his fifth tour-level title of the season after Rome, Wimbledon, Tel Aviv and Astana and now holds a 45-17 career record at the ATP Finals, which he won in 2008 in Shanghai and in 2012, 2013, 2014 and 2015 in London).
"I'm very happy to be able to compete for another big trophy, one of the biggest ones that we have in our sport," said Djokovic.
"Hopefully I'll be able to play at the level that I've played most of the matches this week and get a trophy."