Spain's Carlos Alcaraz will take on Norway's Casper Ruud in the men's singles final at the US Open, with No.1 world ranking also on the line.
The winner will become a major champion for the first time and head the rankings next week.
Alcaraz made it to his first Grand Slam final and earned a chance to become No.1 at age 19 by ending home favourite Frances Tiafoe's run with a 6-7(6), 6-3, 6-1, 6-7(5), 6-3 victory in Friday's second semi-final.
The 23-year-old Ruud beat Russia's Karen Khachanov 7-6(5), 6-2, 5-7, 6-2, winning a 55-shot point to cap the opening set.
World No. 3 Alcaraz moved ahead by grabbing nine of 10 games in one stretch and could have clinched victory when he held a match point in the fourth set.
Tiafoe saved that and forced a fifth set by improving to 8-0 in tie-breakers during the tournament.
Despite playing into the early morning hours in his previous two five-set matches, the 19-year-old Spaniard showed no signs of fatigue on Friday. He fell on his back and covered his face with his hands after winning the hard-fought battle.
If he can beat Ruud, Alcaraz will become the youngest man to be world number one, breaking the mark set by Australian Lleyton Hewitt, who was 20 when he became the world's top-ranked player in 2001.
The win ends Big Foe's run at the tournament, where his unlikely success and uniquely American life story captivated fans and brought out luminaries including former first lady Michelle Obama to Arthur Ashe Stadium on Friday night.
Earlier, Ruud harnessed his mighty forehand to reach his second Grand Slam final this year, keeping alive his hopes of reaching the top of the world rankings.
The first Norwegian man to reach the final at Flushing Meadows won an extraordinary 55-shot rally to close the first-set tie-break on his way to victory at Arthur Ashe Stadium.
"This match is probably the biggest match for both of our careers," said fifth seeded Ruud, who was left humbled when he lost in straight sets to Rafael Nadal in June's French Open final.
"You want to take care of the opportunities you have and I was able to do that today."
The 23-year-old Ruud is known for his poise on clay but was equally effective on New York's hard courts, winning 14 straight points to build a 5-1 lead in a near-flawless second set.
His form deteriorated in the third, where he racked up 11 unforced errors and handed Khachanov the break on set point.
However, Ruud bounced back to convert breaks on chances in the third and fifth game of the fourth set and clinched the contest with a forehand winner, one of 20 across the match.
It took every ounce of his fitness - and a brave face - to survive the affair, as Ruud told reporters his legs were quaking from the marathon first-set point.
"I tried to not show Karen that I'm tired because I don't want him to think that, 'This is tiring for Casper'," he said.
"There is acting in sports. Tennis especially. It's such a mental and psychological game that any small detail can help you win the match."
Ruud will make the leap from world number seven to number one if he hoists the trophy on Sunday over Alcaraz, according to the ATP.