Serena Williams was one point from winning a quarterfinal match in the Australian Open when she turned her left ankle.
It all unraveled from there.
In a startling reversal and result, Williams wasted four match points along the way to dropping the last six games of a 6-4, 4-6, 7-5 loss to No. 7-seeded Karolina Pliskova of the Czech Republic at Melbourne Park on Wednesday.
“I was almost in the locker room,” said Pliskova, who trailed 5-1 in the third set, “but now I’m standing here as the winner.”
So instead of Williams moving closer to an eighth championship at the Open and record-tying 24th Grand Slam tournament title, Pliskova will continue her pursuit of her first major trophy.
In the semifinals, Pliskova will face No. 4-seeded Naomi Osaka, who advanced by beating No. 6 Elina Svitolina 6-4, 6-1.
Williams, 37, trailed by a set and a break at 3-2 in the second when she started turning things around, beginning a run in which she won nine of 11 games.
And then it all changed. Serving for the victory at 5-1, 40-30, Williams was called for a foot fault. During the ensuing point, Williams twisted the ankle and dumped a forehand into the net, and went on to lose that game.
Three more match points followed and Pliskova staved off each one.
“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.”
Williams served for the match at 5-3 and again was broken. She was broken for a third time in a row at 5-5 and Pliskova was on her way to a semifinal meeting with Osaka.
The 21-year-old from Japan stretched her Grand Slam tournament winning streak to 12 matches and moved closer to a second consecutive major championship by parlaying her aggressive and powerful style into a 31-11 edge in winners that helped her put together her victory over Svitolina.
“I tried to be consistent,” the No. 4-seeded Osaka said, “or as consistent as I can.”
Osaka defeated Williams in the U.S. Open final last year but had never been past the fourth round in Australia.
Svitolina had her neck and shoulders massaged by a trainer during a medical timeout while trailing 3-0 in the second set.
The No. 6 seed from Ukraine said she had been troubled by pain in that area since the start of the tournament.
The other women’s semifinal will feature two-time Wimbledon winner Petra Kvitova of the Czech Republic against Danielle Collins of the United States, who had never won a Grand Slam event match before this tournament.
In the men’s doubles quarterfinals, Ryan Harrison and Sam Querrey of the U.S. dropped the first set before winning the next two over seventh-seeded Lukasz Kubot of Poland and Horacio Zeballos of Argentina.