Spanish teenager Carlos Alcaraz ended Frances Tiafoe's amazing run at the US Open with a 6-7(6), 6-3, 6-1, 6-7(5), 6-3 win to reach his first major final, where he will face Casper Ruud with the world number one ranking on the line.
Despite playing into the early morning hours in his previous two five-set matches, Alcaraz no signs of fatigue on Friday. He fell on his back and covered his face with his hands after winning the hard-fought battle.
The 19-year-old Spaniard became the youngest men's Grand Slam finalist since compatriot Rafael Nadal captured the first of his 22 Slams at the 2005 French Open.
Norway's seventh-ranked Ruud earlier defeated Russia's Karen Khachanov 7-6 (7/5), 6-2, 5-7, 6-2 to also reach his first Grand Slam final.
Tiafoe, however, went down fighting by saving three match points and retrieving breaks in both of the last two sets.
"We are in the semi-final of a Grand Slam, we have to give everything we have inside, we have to fight until the last ball," said Alcaraz.
"It doesn't matter if you're fighting for five hours or six hours. It doesn't matter, you have to give everything on court."
For Alcaraz, who unleashed 59 winners, it was his third successive five-setter as he closes in on a maiden Slam and becoming the youngest ever world number one.
"It's my first time in a final of a Grand Slam. I can see the number one in the world, but at the same time it's so far away," he added.
"I'm going to give everything that I have. I will have to handle the nerves of being in the final of a Grand Slam but obviously I'm really happy."
Tiafoe, who received great support from the crowd and whose unlikely success and uniquely American life story has captivated fans, hailed his opponent.
"I gave everything I had, too good from Carlos tonight," said Tiafoe.
"Honestly I came here wanting to win the US Open, I feel like I let you guys down. This one really hurts."
Tiafoe, a 24-year-old from Maryland who eliminated 22-time Grand Slam champ Rafael Nadal in the fourth round, played to a sellout crowd of more than 23,000. No surprise, given he was the first American man in the semi-finals at Flushing Meadows in 16 years.
Meanwhile, Ruud harnessed his mighty forehand to reach his second Grand Slam final this year, beating Russian Khachanov.
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 Ruud.
"You want to take care of the opportunities you have and I was able to do that today."