The two highest seeds from the top quarter, top-seeded Simona Halep and sixth-seeded Karolina Pliskova, advanced to the quarterfinals Monday, setting up a quarterfinal showdown Wednesday.
Wednesday’s other quarterfinal will feature Angelique Kerber, the 2016 champion here, against Madison Keys, last year’s U.S. Open runner-up.
Halep defeated Naomi Osaka, 6-3, 6-2, showing few ill effects from her marathon 4-6, 6-4, 15-13 win over Lauren Davis two days earlier, a match that lasted close to four hours. Well-earned soreness from that match, Halep said, had set in about 36 hours after it finished.
“Last night was really tough,” she said. “I couldn’t sleep. I had pain everywhere.”
But a nap Monday afternoon gave her a boost, as did her growing acceptance of the discomfort she has felt since badly rolling her left ankle during her first-round victory a week ago.
“I’m trying to play 100 percent — which I was close today — to run normal, and to run a lot,” Halep said. “But I still feel it. It’s there, but I can handle it.”
In the last match of the day’s schedule, which stretched more than an hour into Tuesday morning, Pliskova won, 6-7 (5), 6-3, 6-2, over 20th-seeded Barbora Strycova, a fellow Czech.
Pliskova hired away Strycova’s coach, Tomas Krupa, in the offseason, which Strycova countered by hiring Pliskova’s previous coach, David Kotyza. The swap led to a frosty atmosphere at the Prague club where they both trained, but the players were able to keep that subplot on the sidelines in their first encounter since the changes.
“I was just trying to play my game,” Pliskova said. “Because I know if I would get into it and think about what everything happened with the coaches and with her, I would not be playing the best. I think this I did perfect. I was just really focused on my tennis, not on the things around.”
That composure led the Open’s on-court interviewer, Rennae Stubbs, to describe Pliskova as “cool as a cucumber.” The idiom bemused Pliskova, who later said that she would have to turn up the heat of her game in order to hit through Halep’s relentless defenses in the next round.
“I have to get my mindset ready for this,” Pliskova said.
There will be a similar challenge for Keys against Kerber, in a comparable battle of puncher versus counterpuncher.
“I think she has an ability to cover the court and anticipate like really no one else does,” Keys said of Kerber. “So, for me, it’s having to play aggressive but also consistently aggressive, because I know she’s going to make three more balls than other girls may be able to get to.
“So it’s not feeling rushed and that I have to go for something crazy-big on the first one. Just really work the point.”
Kerber, who has won six of seven matches against Keys, appeared burdened by the No. 1 ranking she carried for much of last year. This year, seeded 21st, she has played more freely, and she will be seeking her 14th consecutive victory.
“I just enjoy my tennis again,” Kerber said. “I think this is the most important thing for me when I’m on court: that I fight, that I play my game.”
The bottom half of the draw produced an unexpected semifinalist later Tuesday, when the unseeded Elise Mertens routed No. 4-seeded Elina Svitolina, 6-4, 6-0, to reach the final four of a major tournament for the first time. Mertens will face the winner of the match between No. 2-seeded Caroline Wozniacki and Carla Suárez Navarro later Tuesday.
This article originally appeared in The New York Times.