World No.1 Iga Swiatek has won a service break-laden clash with American Jessica Pegula to set up a US Open semi-final against sixth seed Aryna Sabalenka.
The winner of two French Open grand slam titles, 21-year-old Swiatek boosted her quest for a hard-court slam breakthrough in New York with a 6-3 7-6 (7-4) quarter-final win on Wednesday night.
The match was filled with a combined 13 breaks of serve, 10 in the second set alone, and Swiatek twice failed to serve out the victory, at 5-4 and 6-5.
But the Polish star was better in the tiebreaker, and when eighth seed Pegula missed a backhand, Swiatek flung her racquet away and yelled after reaching her maiden US Open semi.
Swiatek will now face Belarusian Sabalenka, who downed Karolina Pliskova 6-1 7-6 (7-4) earlier.
Thursday's other women's semi-final is fifth seed Ons Jabeur against 17th seed Caroline Garcia.
Swiatek compiled a 37-match winning streak earlier this season, claiming the trophies at six consecutive events, but this is her first trip beyond the fourth round in New York.
"I wasn't expecting that at the beginning of the tournament," she said. "Trying to keep my expectations low."
It was Swiatek's eighth win in a row against an opponent ranked in the top 10, all in straight sets.
"I'm super proud of myself. My goal, basically, is to be consistent," she said. "I remember when I was an underdog and every match like that was surreal."
Of the four players remaining, only Swiatek already owns a slam title. And only Sabalenka has been this far in New York previously; she lost in the semi-finals last year.
"I'm ready for it," Sabalenka said. "I'm ready for another fight."
Sabalenka, who trailed Kaia Kanepi 6-2 5-1 in the second round, will be attempting to reach her first career grand slam final. She lost to Pliskova in the last four at Wimbledon last summer.
This year, Sabalenka could not participate at the All England Club, because all players from Russia and Belarus were banned over the invasion of Ukraine.
"It was tough time, especially when I was working out in the gym and there was Wimbledon playing on the TV. I was always turning it off because I couldn't watch it," said Sabalenka.
""They took away one opportunity from me and I worked really hard for this one."