Iga Swiatek dropped to her knees on the court and clutched at her midsection after getting hit by a ball during a point in the Paris Olympics singles quarterfinals Wednesday, but it was her opponent, Danielle Collins of the United States, who stopped playing later in the third set.

Swiatek was leading 6-2, 1-6, 4-1 when Collins retired from the match after taking a medical timeout then getting another visit from a trainer.

Collins, a 30-year-old who was the runner-up at the 2022 Australian Open and has announced she will retire from elite-level tennis after this season, said she cramped and went into convulsions because of dehydration and exhaustion after competing in heat that reached 97 degrees Fahrenheit on Tuesday.

She blamed Olympic organizers for not having insulated water bottles, for the water not being cool enough and for not “prioritizing the health of the athletes.”

In the opening game of the final set, with Collins serving at deuce, she directed a backhand down the middle of the court. Swiatek was up at the net and unable to get out of the way of the shot.

Swiatek looked stunned as she let go of her white racket and stopped down on the red clay at Court Suzanne Lenglen. Collins — who asked, “Iga, are you OK?” — walked around the net to check on Swiatek, and chair umpire Damien Dumusois climbed out of his perch to see how the world’s No. 1 player was.

“I could not breathe for a moment. It hurt for a bit,” Swiatek said. “But with the adrenaline that you have on court, you don’t feel as much as you should.”

Swiatek eventually rose and nodded to indicate she could continue.

Three points later, Collins pushed a forehand long and Swiatek had a break. Soon, she would break again to lead 3-0 in that set, and Collins left the court for a medical timeout that delayed the action for about five minutes. When they resumed, it quickly became 4-0, before Collins took a game. But then she conceded the match.

In the semifinals, Swiatek will face Zheng Qinwen, who ended the stellar career of Germany’s Angelique Kerber in a titanic tussle that ended 6-7 (4), 6-4, 7-6 (6).

Zheng failed to convert three successive match points in the third set as Kerber clung on grimly in stifling heat but eventually prevailed, collapsing to the red clay in disbelief as Kerber’s last shot struck the net.

Kerber, a three-time Grand Slam champion, announced last week she would retire after the Olympics.

“I’ve achieved everything I dreamt of,” Kerber said. “I was No. 1, won Grand Slams, won a [silver] medal in Rio, so what more could you want in the end?”

Wimbledon champion Barbora Krejcikova of the Czech Republic bowed out with a 6-4, 6-2 loss to Anna Karolina Schmiedlova. Schmiedlova has now eliminated both women who played in the final at the All England Club 2½ weeks ago. She defeated Wimbledon runner-up Jasmine Paolini in the third round Tuesday and now is the first tennis semifinalist from Slovakia at a Summer Games since 1988.

Krejcikova was seeded ninth in Paris and has fared well on the clay courts at Roland Garros, which hosts the French Open and is being used for tennis at these Olympics. Her first Grand Slam singles championship came at the French Open in 2021, when she also won the doubles title.

But with the heat at 90 degrees Fahrenheit and the air thick with humidity, Krejcikova looked listless down the stretch against Schmiedlova, a 29-year-old who is ranked 67th and owns one fourth-round appearance at a Slam. That came last year at Roland Garros.

By the end, Krejcikova appeared spent and was barely moving. She slapped a forehand into the net to finish the match, and Schmiedlova raised both arms overhead.

The two players accumulated nearly the exact same number of winners, with 18 for Krejcikova and 17 for Schmiedlova. The big difference was in unforced errors: 32 by Krejcikova, more than twice as many as Schmiedlova’s 15.

That included five double-faults for Krejcikova, who needed to deal with 11 break points and lost five of her service games.

Next for Schmiedlova will be a match Thursday against Donna Vekic of Croatia, who beat Coco Gauff in the third round, or Marta Kostyuk of Ukraine, with a place in the gold medal final on the line.

The Associated Press and Reuters contributed to this report.