“Then, suddenly, I got a chance too,” Pliskova said of her improbable victory after facing four match points. “That’s how it is in tennis. You need luck, of course, because this is — I think — not happening often. Maybe once in life. But I went for it.”

Williams, who like all right-handers lands on her left foot when she serves, lost all 10 remaining points on her serve after the injury. While she said she would not know how bad her ankle injury was until a day later, she played down the effect of the injury on the outcome of the match, repeatedly giving Pliskova credit for playing “lights out” tennis as she surged back.

“I think she just played well on my serve after that point,” Williams said. “I think she just kind of started playing really, really good. I don’t think it had anything to do with my ankle, per se. I just think she was just nailing and hitting shots. Obviously I made some mistakes, but she played really well after that.”

Pliskova said she thought something might have happened to Williams, but that she remained focused on her own side of the court.

“Whatever is happening on the other side, I just try to block it,” Pliskova said. “Either it’s positive or negative, whatever is there, it’s just not my business. I’m sorry, but that’s how it is. I know once I’m starting to think about that, it’s bad.”

Pliskova won the next two games to complete the improbable comeback, winning after Williams hit a forehand into the net for an unforced error on her third match point.

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 had looked on track for a similarly efficient victory when she broke Williams for a 3-2 lead in the second set.