Top seed and defending champion Naomi Osaka crashed out of the US Open in the fourth round after a straight-sets defeat by Belinda Bencic.
Osaka has been carrying a knee injury and called the trainer and a medic on midway through the second set, although she was able to carry on without receiving any treatment.
However, the 21-year-old from Japan was beaten 7-5 6-4 by the Swiss 13th seed.
Her defeat came just a day after men's champion Novak Djokovic also bowed out after retiring at two sets down to Stan Wawrinka.
Osaka was cheered to the rafters as she trudged off court, a crowd favourite now after the way she consoled American youngster Coco Gauff following their match on Saturday night.
It was a third straight win for Bencic over Osaka this year, and she said: “The challenge cannot be bigger against Naomi, she won this title last year.
“I’m really pleased with my game and how I handled my nerves.
“I tried taking the serve early and trying to anticipate, because she has a lot of power. I don’t hit so many winners. I try to play it a little bit like chess.
“I was in the stadium watching the [Gauff] match and thought it was an unbelievable moment for tennis. What Naomi did is what a true champion would do.”
Bencic will play Donna Vekic in the quarter-finals after the Croatian came from a set down to beat Julia Goerges of Germany.
Goerges had a match point in the second set but ended up losing 6-7 (5) 7-5 6-3.