Wimbledon champion Marketa Vondrousova moved a step closer to back-to-back grand slam titles by beating Peyton Stearns to reach the US Open quarter-finals.
The 24-year-old Czech, seeded ninth here two months after becoming the first unseeded woman to win at SW19, fell a set behind to Stearns.
But the American youngster, whose powerful forehand accounted for Britain's Katie Boulter in round three, won just five more games as Vondrousova triumphed 6-7 (3) 6-3 6-2.
"She was playing great from the beginning and I just tried to stay in the game," said Vondrousova.
"She is a very dangerous player, she has a great future ahead of her and it was a very tough match.
"I'm very happy. I didn't expect this, after Wimbledon there was a lot of pressure but I'm feeling good and we'll see what happens next."
What happens next is a meeting with Madison Keys, a former Flushing Meadows runner-up who sprung a mild surprise against fellow American Jessica Pegula, the third seed.
Keys, seeded 17, is emulating the form which swept her to the final in 2017 and sunk the highly-fancied Pegula 6-1 6-3.
The 28-year-old said: "It's always tough having to play a friend but we've been doing it all our lives. On court it's all business but then we go back to being friends."
Second seed Aryna Sabalenka eased past Daria Kasatkina 6-1 6-3 to make the quarter-finals for the third year in a row, subduing her opponent with her powerful forehand inside Arthur Ashe Stadium.
Australian Open champion Sabalenka will rise to the top of the WTA rankings when they are updated after the tournament and was playing with the confidence of a world number one as she pounded Kasatkina with 31 winners.
Kasatkina lost in straight sets to the Belarusian last month in Cincinnati and had clearly not cracked the code, as Sabalenka overwhelmed her at every turn.
Sabalenka next faces China's Zheng Qinwen, who knocked out 2022 finalist Ons Jabeur in straight sets.
The Tunisian, who has struggled physically all week after illness, bowed out 6-2 6-4.
Second seed Sabalenka said her opponent will have nothing to lose in their first meeting.
"She played great tennis against Ons. I haven't watched her previous matches," Sabalenka said.
"The trickiest part is that she's moving well, playing some heavy shots. I have to be physically and mentally ready that it's going to be some winners against me in that match.
"I just have to focus on myself more than on her, on my game. I know if I'll bring my tennis there, I have chance to win this match."
Additional reporting: Reuters
