World number one Jannik Sinner beat former champion Daniil Medvedev in a topsy-turvy US Open match to set up a semi-final against Jack Draper.
Italy's Sinner was a 6-2 1-6 6-1 6-4 winner over the Russian fifth seed in New York.
Sinner, who won the Australian Open in January, and Medvedev were the only two major champions left in the men's draw and the match between them was highly anticipated.
However, neither men were able to find their best tennis at the same time.
Medvedev, a beaten finalist at Flushing Meadows last year and in 2019, hit six double faults and sprayed 57 unforced errors
While Sinner was not at his most accurate, he was far superior on serve, closing out victory in two hours and 39 minutes.
Sinner will now face his occasional doubles partner Draper in Friday's semi-final.
"We know each other very well, we are good friends off the court," Sinner said of Draper.
"It's going to be very tough - I'm just happy to be in the semis."
There is now guaranteed to be a first-time US Open winner in both the men's and women's singles, with Americans Taylor Fritz and Frances Tiafoe contesting the second men's semi-final.
Sinner and Medvedev have met at three of the four Grand Slams this year, but this match did not fully reach the high quality of their previous outings.
Sinner came back from two sets down against Medvedev to win his maiden Grand Slam title in Melbourne, while Medvedev got his revenge in another five-set match in the Wimbledon last eight in July.
Asked to serve first, Medvedev was immediately under pressure, having to save a break point before being broken to love a few games later.
Sinner barely missed a step on serve before the start of the second set, when he was drawn into the longer rallies that Medvedev thrives on.
The Russian went up an early break and doubled his advantage after a 10-minute game on the Sinner serve which ended with the Italian dumping a forehand into the net.
With the match level, the momentum swung towards Sinner, who reeled off five games in a row and had three set points on the Medvedev serve to register a dreaded 'bagel'.
Medvedev managed to scrape one game in the third set and went off court to regroup, but immediately had to recover from 0-30 down in his first service game and a break of serve felt inevitable.
Once Sinner secured the decisive break for a 4-3 lead, his quality came through, with victory secured with a stunning forehand winner.
Sinner has lost only two hard-court matches this season and won four titles on the surface, including his Australian Open triumph.
His most recent success was at Cincinnati in August, winning the title the day before news emerged he had been cleared of any wrongdoing after twice testing positive for a banned substance earlier this year.
BBC