MELBOURNE, Australia — Serena Williams was one point from the Australian Open semifinals when she lost her footing and the match slipped away.
Williams, who was seeking a record-tying 24th Grand Slam singles title, lost the final six games to fall, 6-4, 4-6, 7-5, to Karolina Pliskova on Wednesday, relinquishing her lead after rolling her left ankle when the match was within her reach.
Pliskova, in her on-court interview afterward, acknowledged how close the match had been: “I was almost in the locker room, but now I’m standing here as a winner,” she said. “So it’s a really good feeling.”
It wasn’t clear from Pliskova’s remarks immediately after the match whether she had noticed Williams’ ankle trouble, but she did observe a drop in her play.
“She got a little bit shaky in the end,” Pliskova said of Williams. “So I took my chances and I won.”
Pliskova, the No. 7 seed, will face the fourth-seeded Naomi Osaka in the semifinals on Thursday. The other semifinal pits the eighth-seeded Petra Kvitova against the unseeded American Danielle Collins.
This was Williams’s fourth major tournament since resuming her career in 2018 after the birth of her daughter, Alexis Olympia Ohanian Jr., in September 2017. Williams withdrew before the fourth round of last year’s French Open because of an injury and lost in two other Grand Slam finals — to Anqelique Kerber at Wimbledon and to Osaka at the United States Open in a match remembered primarily for Williams’s confrontation with the chair umpire that cost her a game penalty.
Williams, who dispatched the top-seeded Simona Halep in a hard-fought, fourth-round match, has not defeated two top-10 players at the same event since returning from her pregnancy. She has spoken candidly about her struggles to return to peak physical condition after giving birth, but she arrived here looking fitter than she had since before her pregnancy.
Her match on Wednesday turned in an instant. With a commanding 5-1 lead in the third set, the 16th-seeded Williams held a match point on her serve, at 40-30. But after she was called for a foot fault on her first serve, Williams appeared to sustain an injury in the rally that began off her second serve, rolling her left ankle as she tried to change directions to reach a shot from Pliskova.
Williams lost the point, and then the next two points. She did not call a medical timeout on the ensuing changeover, but she retied her shoelaces, making them tighter.
But the tighter shoes did not keep her in the match. Pliskova won the next two games, pulling to 4-5, suddenly back on serve. Williams earned three more match points in the 10th game, but Pliskova saved them all. Pliskova held to make it 5-5 with a backhand cross-court winner, punctuated with a loud and long scream.
She won the next two games to complete the improbable comeback, winning after Williams hit a forehand into the net for an unforced error.
Pliskova, a former No. 1, had knocked Williams out of a Grand Slam event before, beating her in straight sets in the 2016 United States Open semifinals. She looked on track for a similarly efficient victory when she broke Williams for a 3-2 lead in the second set.
But Williams roared back, breaking Pliskova at love in the next game. Williams won 10 of the next 12 games, taking complete command of the match before her late collapse.
Pliskova, whose appearance in the 2016 United States Open final was her only previous major title match, has won two of her previous three matches against Osaka. She most recently beat her, 6-4, 6-4, in the final of the WTA tournament in Tokyo in September.
Osaka, 21, will be seeking a second straight Grand Slam title. She reached the semifinals with a 6-4, 6-1 win over the sixth-seeded Elina Svitolina.
Osaka, who had never reached the quarterfinals of a Grand Slam before her triumph in New York last fall, said she was keeping this accomplishment in perspective.
“To be here is something that a lot of people want, and I know that a few months ago I would have given anything to be in the semifinals of a slam,” Osaka said. “But it’s this weird feeling of: You want to do the next big thing. And especially now that I won a Grand Slam, and I feel like I want to win another one, and I’m so close and I just want to keep going.”
Osaka and Kvitova could each claim the No. 1 ranking for the first time if they win the tournament on Saturday. After pulling herself from the brink of defeat, Pliskova also has a chance to return to the No. 1 ranking with a win, even if she had begun to count herself out of the tournament when she was one point from defeat.
“My mind was in the locker room,” Pliskova said. “I was still here.”