Kei Nishikori produced a remarkable physical feat to defeat Stan Wawrinka in five sets and become the first Japanese man in the Open era to reach a grand slam semi-final.
Tenth seed Nishikori had beaten Milos Raonic in the fourth round in five sets in a match that finished at 2.26am - the joint latest finish in US Open history.
He was back on Arthur Ashe Stadium barely 36 hours later and battled for another four hours and 15 minutes to put out the Australian Open champion 3-6 7-5 7-6 (9/7) 6-7 (5/7) 6-4.
The last Japanese man to make the last four at a grand slam was Jiro Satoh at Wimbledon in 1933.
Nishikori said: "I started a little bit tight but my body was okay, I was feeling more and more confident, especially getting the third set. I don't know how I finished the match but I'm very happy.
"I feel amazing. This is my favourite grand slam. I have good memories here and I'm very happy to be first time in the semis. I hope I can recover again and play 100% tennis next round."
Given Nishikori's exertions, it was no real surprise when Wawrinka raced into a 3-0 lead, and that was enough for the Swiss to take the opening set.
But Wawrinka, who put on a masterclass against Andy Murray at the same stage last year to reach his first slam semi-final, has not been on top form this tournament and it was the same again.
The 29-year-old was making bad mistakes at bad times, none more so than the double fault that handed Nishikori the second set.
Far from tiring, the Japanese player seemed to be improving as the match went on, his forehand in particular keeping Wawrinka on the run.
Nishikori made his move in the sixth game of the third set with a break of the Wawrinka serve and had a set point at 5-2 but could not take it.
And that looked a huge moment in the following game when Nishikori made a complete mess of serving for the set and lost his advantage.
The 24-year-old collected himself to force a tie-break and had another set point on his own serve only for Wawrinka to thread a brilliant backhand pass down the line.
A vicious forehand gave the Swiss a chance to clinch it but Nishikori responded in kind with a stunning backhand winner of his own.
These were huge moments in the match, and it was Nishikori who came out on top, Wawrinka going long with his 55th unforced error.
The toll on Nishikori showed after three games of the fourth set when he took a medical time-out to have his blisters treated but he continued to play high-level tennis to keep pace comfortably with Wawrinka.
Nishikori fought back from 4-0 down in the tie-break to level at 4-4 but missed two forehands wide and Wawrinka landed a huge second serve on the back of the line to level proceedings.
With the match well into its fourth hour, they headed into a decider, and it was Wawrinka who finally cracked, serving a double fault to give up two match points at 4-5.
He saved the first but netted a forehand on the second to send Nishikori, who is coached by former French Open champion Michael Chang, into the last four.