(CNN)World No.1 Rafael Nadal beat Dominic Thiem in a grueling five-set quarterfinal, recovering from a disastrous opening set to clinch the match in dramatic style.
Finishing just after 2 a.m local time, the defending champion saw off his younger Austrian opponent 0-6 6-4 7-5 6-7 (4-7) 7-6 (7-5) in what was his longest match at the US Open.
Top seed Nadal said "suffering" was the "right word" to describe the 4 hour, 48 minute contest.
"It's been a great battle, the conditions were tough, a lot of humidity. It was a very tough start, I tried to stay in the match in the second set," the Spaniard said on court.
"I just (kept) going, I'm very sorry for Dominic, he's a close friend on tour, a great guy, and I wish him all the very best.
"He's young, he has plenty of time to win big tournaments. He's a fighter, he has a great attitude. I'm sure he will have his chances in the future."
The 32-year-old Nadal, a three-time champion at Flushing Meadows, will play third seed Juan Martín del Potro in the semifinals.
Nadal was overpowered by ninth seed Thiem -- the only man to beat him on clay for the last two seasons -- in the first set as the 25-year-old hit 13 winners and made only two unforced errors in an extraordinary start.
But the 17-time grand slam champion battled back to win the second and third sets before Thiem came out on top of an 81-minute fourth set to take the match into a nerve-wracking decider.
At 5-5 and 0-40, Thiem saved all three break points and forced the fifth set into a tiebreak, but it was Nadal who came out on top when the Austrian sent a smash long.
It meant the Spaniard avoided following world No.2 Roger Federer, who surprisingly lost to world No.55 John Millman Monday, out of the competition.