Defending champion Rafael Nadal overcame a first set shutout to beat Dominic Thiem in the longest match of this year's US Open.
Nadal won the four hour 49 minute quarter-final epic 0-6 6-4 7-5 6-7 (7-4) 7-6 (7-5) on Wednesday (NZ time).
It was only the fourth time in 282 career grand slam matches that Nadal lost a set by a 6-0 score. It's the first time he won the match after that kind of start.
Nadal also trailed by a break in the third set before taking it against the Austrian. He came within two points of victory late in the fourth set before being pushed to a fifth, where he was two points from a loss.
But the Spaniard held on and is into the semi-finals at a third consecutive major tournament as he bids for a fourth US Open title and 18th grand slam trophy overall.
Nadal will meet Juan Martin del Potro in a semi-final.
Del Potro outslugged John Isner in four sets after a towering battle in a sweltering Arthur Ashe Stadium.
The two big men battered each other to near exhaustion in the heat and humidity but it was the Argentine third seed who proved the stronger to prevail 6-7 (5-7) 6-3 7-6 (7-4) 6-2 in three-and-a-half hours.
With the mercury hitting 35C and humidity at about 50 per cent, the US Tennis Association invoked its new extreme heat policy, which allowed the players to take a 10-minute break after the third set -while officials called a halt to junior matches on the outside courts for more than two hours.
"I'm so happy to reach another semi-finals in my favourite tournament," del Potro said in his on-court interview.
"That's very special to me. Beating John in these kind of matches is like an epic, an epic match.
"We both were tired in the end, we both fought until the end and I think I survived with my serve.
"That was the only difference I think."