Sixth-seed Aryna Sabalenka has bounced back from a slow start and visits from the trainer to beat the No.19 seed Danielle Collins 3-6 6-3 6-2 and reach the US Open quarter-finals.
Sabalenka continued her mastery at Flushing Meadows over American Collins, beating her for the third time at the US Open (2018 and 2021).
"I was just trying my best. I was trying to serve well. I was trying to make her move. I was just trying to stay in this match as much as I could," Sabalenka, who improved to a spotless 4-0 overall record against Collins, said.
"She played unbelievable tennis. It was a crazy level today. I'm super happy with the win. She's tough to play against."
An Open semi-finalist in 2021, Sabalenka led 4-3 in the second set when she needed a medical timeout and had a trainer massage her left thigh throughout breaks on Arthur Ashe Stadium.
Sabalenka, who is from Belarus, was not allowed to play at Wimbledon this year after all players from her country and Russia were banned because of the invasion of Ukraine.
She'll face the 22nd seed Karolina Pliskova in the last eight after the Czech enjoyed a 7-5 6-7 (7-5) 6-2 win over 26th seed Victoria Azarenka.
Pliskova, a former world No.1, was the 2016 runner-up in New York and at Wimbledon in 2021 and scored a fifth victory in nine matches against Azarenka.
"It's always a tough match against her," Sabalenka, an even 2-2 against Pliskova, said.
"But it's another fight, and I'm ready for it. Whatever happens, I'll be ready."
Earlier in the day, it took a while for world No.1 Iga Swiatek to get going and fire her way into the last eight.
There she will meet the No.8-seeded local Jessica Pegula, who brushed aside two-time Wimbledon champion Petra Kvitova 6-3 6-2 to reach her third major quarter-final of 2022.
Swiatek beat Germany's Niemeier 2-6 6-4 6-0, but is clearly not in the form that brought her 37 straight wins earlier this season.
Swiatek came into the US Open just 4-4 in her last eight matches but she hadn't lost a set in New York until Monday. She became the first Polish woman to reach the US Open quarters and is trying to become the first top-seeded woman to win it since Serena Williams in 2014.
"I'm just proud that I didn't lose hope because she was playing really good in the first set," Swiatek said.
"I'm pretty glad that I used my experience to keep the same kind of level throughout the whole match."
Pegula is 0-3 in grand slam quarter-finals, including losses at that stage at the Australian Open in January and the French Open in June. The loss in Paris came against Swiatek.