A US Open that began with Serena Williams's farewell tour could end with a coming-of-age party for tennis's brightest young star.
By overcoming Frances Tiafoe in five sets on Friday, 19-year-old Spaniard Carlos Alcaraz has set up a compelling script on Sunday night, when he faces Casper Ruud, the understated Norwegian, in a final that will decide who becomes world No 1.
It is the neatest of conclusions and a wonderful backdrop for that tipping point we have been talking about for five years or more: the long-awaited "changing of the guard".
Alcaraz's progress has been bewildering in so many ways. Not least because he has come through three successive five-setters, against Marin Cilic, Jannik Sinner and now Tiafoe.
His cumulative time on court already stands at 20 hr 19 min, which means that, if he were to win the final, he would almost certainly set a grand-slam record for the hardest-earned major title. Again, Nadal is the man to beat here, having battled away for 22hr 28min at January's Australian Open.
But Alcaraz's apparently limitless endurance is only the beginning. Had he chosen virtually any other sport, he would surely have succeeded just as brilliantly, given that he also has a robust mental game and what must surely be the most explosive, lickety-split movement seen in tennis. After Friday's semi-final, Tiafoe - who has played all the so-called "Big Three" - said: "I never played a guy who moves as well as him."
Alcaraz redefines the logic of the game by apparently teleporting across the court.
At one stage on Friday, he played one of his patented forehand drop shots to bring Tiafoe into the net, but the pair exchanged six successive dinks of ever-increasing genius.
At the conclusion of one of the most inventive rallies you will ever see, Alcaraz sprinted back like the Looney Tunes Road Runner and rifled a forehand pass down the line to draw the biggest roar of the fortnight - and this against the local boy.
If we are forgetting about Ruud here, then we are not the only ones. While Alcaraz dominated the second week's night sessions - enduring the US Open's latest finish, at 2.50am, on Wednesday night - Ruud has barely made a ripple with his seamless progress. Quietly dispatching a series of dangerous opponents, he has been a stealthy soldier in the night, a tennis ninja.
It has been the same story all year for Ruud, an apparently slight figure at just 6ft and 170lb, who nevertheless owns a deceptively-lethal forehand and a serve that - because of its sudden, whipcrack action - is almost impossible to read.
These two lead the standings for the most wins over the past 12 months, with 60 for Alcaraz and 61 for Ruud, who has more than earned his shot at the world No 1 ranking. Yet Ruud makes his progress in such a way - clean-cut and controversy-free - that few floating sports fans have seen him coming.
All that will change if Ruud should cash in on his economical ride to the final - bear in mind that he has spent around four-and-a-half fewer hours on court in the past week than Alcaraz - and score his first major trophy.
We will learn more about his father and coach, Christian, himself a top-40 player in the 1990s, and the transformational effect of joining Nadal's academy in Majorca as a 19-year-old.
At that stage, Ruud - then the same age that Alcaraz is now - was ranked No 143 in the world. But his regular practice sessions with Nadal, and the advice he has absorbed from Toni Nadal - Rafael's uncle, who now coaches Felix Auger-Aliassime - helped him upgrade his game and his mentality.
So it is that we arrive at this perfectly scripted conclusion to a magnificent US Open. Indeed, here is an unprecedented scenario. Players have gone into major finals with the world No 1 ranking on the line before, but never two relative newcomers, both looking to grab that top spot for the first time.
The worry for Ruud, and for everyone else in the locker-room, is that the final could be the beginning of an Alcaraz era that lasts for years. Should Alcaraz win, he would become the youngest No 1 since rankings began, shattering a record held by Lleyton Hewitt at 20 years 268 days.
Alcaraz is just 19 years 128 days old and already deadly on any court. Sooner or later, he seems certain to become the pre-eminent figure in the game.