Ben Shelton beat defending champion Carlos Alcaraz 6-7(5) 6-1 6-3 1-6 7-6(10-7) in the early hours of Wednesday to reach the semi-finals of the US Open in the latest-finishing match in tournament history.
Shelton's win sets up a match in the last four with compatriot Frances Tiafoe, boosting home hopes of a first American men's Grand Slam champion since 2003.
Seven-times major champion Alcaraz arrived at Arthur Ashe Stadium with a 13-0 Grand Slam record against US men but found Shelton tough to break down in a match that began at 11.05 pm on Tuesday and finished at 3.33 am on Wednesday.
"For me it's always about the people in the crowd," Shelton said in explaining how he got through the gruelling contest. "Whether it's my coaches and my team there, all my family and friends here, or the city of New York that showed up tonight till 3 am with the USA chants until the very end.
"That's what kept me going, and that's what got me this win tonight.
"It's incredible. I always say that this is the greatest sports city in the world. I say that this is the greatest stadium in the world."
Alcaraz clinched a tight first-set tiebreak and looked to have all the momentum but uncharacteristic sloppiness allowed Shelton to breeze through the next set before the American tightened his grip on the quarter-final by taking the third.
The Spaniard, making his comeback in New York after nearly five months out with a wrist issue, looked flat and made far too many unforced errors on his forehand but still managed to force a deciding set amid roars from the delighted fans.
Alcaraz vomited into a towel during the break but went toe-to-toe with Shelton for 12 games before his opponent closed out the shock win after four hours and 28 minutes.
"I'm hoping that my best friend and my sister up there don't have to be at work in three hours," Shelton added. "It would be huge from their employers to let them have the day off today.
"To be here in front of you guys tonight is an absolute honour. Sharing the court with Carlos is an absolute honour, and I cherish every moment I have out here."

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