NEW YORK (AP) -- Lesia Tsurenko leaned on her racket, looking like she was about to collapse.
The medical team had already asked if she wanted to stop, and this time Tsurenko was thinking about it.
"At some point," she said, "I just thought that it's over for me for today."
Doubled over between points, not even running during some of them, Tsurenko said she was dizzy, unable to deal with the heat that returned to the U.S. Open on Monday after a brief comfortable spell.
"I don't think she was struggling so much," Marketa Vondrousova said. "She was just acting."
The aching -- or acting, according her opponent -- Tsurenko eventually pulled out a 6-7 (3), 7-5, 6-2 victory to reach her first Grand Slam quarterfinal.
The high temperatures that baked the courts at Flushing Meadows last week were back, with U.S. Open officials reinstituting the extreme heat policy that allowed women to take a 10-minute break between the second and third sets, and men to do so between the third and fourth.
But even the players who got off the court fairly quickly had a tough time while they were playing with temperatures in the low-90s Fahrenheit (mid-30s Celsius) that are expected to remain at least through Tuesday.
"It's not easy to play in these kind of conditions," Novak Djokovic said after winning his fourth-round match in straight sets. "At the same time, you can't do anything but try to be tough and survive, you know, find a way to win."
That's what Tsurenko was telling herself.
The Ukrainian didn't know why she was struggling so much, because it wasn't as hot as her first-round match last Tuesday, when six players quit their matches, with five citing cramps or heat exhaustion.
Her temperature and blood pressure were checked during a medical timeout when she led 5-4 in the first set.
"The physio asked me a few times if I want to stop," Tsurenko said. "She saw that I cannot breathe well. She said something (was) wrong that my eyes were -- I don't know what she said exactly, but something wrong with my eyes. She thought I cannot play. She asked me a few times if I want to stop."
Tsurenko bent over between points in the first-set tiebreaker, left the court for more treatment after losing it, and then fell behind 2-0 in the second. It was about then that she considered quitting, though Vondrousova didn't believe it.
"I wasn't like, 'Oh, she's going to retire,' or something. I knew she was going to play normal," said the teenager, who got treatment after the second set.
Tsurenko, who upset No. 2 seed Caroline Wozniacki in the second round, faces No. 20 Naomi Osaka in the quarterfinals. She said she was proud of herself for what she overcame to get there.
"As a tennis player, I know that we play in different type of conditions," she said. "Sometimes it goes like this. You need to survive."