Fifth seed Alexander Zverev defeated Borna Coric in four sets to reach the US Open semi-finals on Tuesday.
The German overcame the 27th-seeded Croatian 1-6, 7-6 (7/5), 7-6 (7/1), 6-3 in 3hr 25min inside Arthur Ashe Stadium.
Zverev, seeking a maiden Grand Slam title, will play either 12th seed Canadian Denis Shapovalov or Spain's 20th seed Pablo Carreno Busta for a place in the final.
The 23-year-old Zverev said he stepped on the gas after finding himself a set down, and 4-2 behind in the second set.
"I just started playing maybe a little bit more aggressive because if I would have played the way I played it's not the level for a quarter-final match of a Grand Slam," he said.
"I just started playing better. I was a little bit more consistent and as well, my serve got better.
"I thought to myself I'm down 6-1, 4-2, I have nothing to lose at the moment," Zverev added.
Zverev performed well when kept his first serves in play. He smashed 18 aces, while the 23-year-old Coric could only make five.
The world number seven struggled with consistency at times, however.
He hit 12 double faults, ten more than Coric.
Zverev won 76 percent of first serve points compared to just 41 percent on his second serve.
The German hit far more winners than the Croatian though, 52 to 37.
It was a close contest, with Zverev accumulating 136 points in total, just four more than Coric.
The disqualification of top seed Novak Djokovic on Sunday blew the men's competition at Flushing Meadows wide open.
His departure means the US Open will crown a first-time Grand Slam winner on Sunday.
In Wednesday's quarter-final matches, second seed Dominic Thiem plays Australia's Alex de Minaur and third seed Daniil Medvedev takes on Russian compatriot Andrey Rublev.