Serena Williams says she "did not choke" after missing four match points as Czech seventh seed Karolina Pliskova won the final six games to win a dramatic Australian Open quarter-final.
The 37-year-old American, going for a record-equalling 24th Grand Slam singles title, led 5-1 in the decider but lost 6-4 4-6 7-5 in Melbourne.
"I think she just played lights out on match points," Williams said.
"I took my chances," said Pliskova who won on her third match point.
Former world number one Pliskova will meet Japan's fourth seed Naomi Osaka in the last four on Thursday with eighth seed Petra Kvitova taking on unseeded American Danielle Collins in the other semi-final.
Williams, seeded 16th, played down an ankle injury which she suffered during the rally on her first match point when serving at 5-1, 40-30.
The seven-time Australian Open champion did not win another point on serve after the incident.
"She was hitting lines and went crazy. She played unbelievable on match points," Williams said.
"It was nothing to do with my ankle. Obviously I made some mistakes but she played really well."
Williams' inability to seal victory means a highly anticipated rematch of her controversial US Open final defeat by 21-year-old Osaka must wait.
Like Osaka, Pliskova will be playing in the Australian Open semi-finals for the first time and is one victory from appearing in her second Grand Slam final, following defeat by Germany's Angelique Kerber in the 2016 US Open.
Pliskova had led by a set and a break at 3-2 before the momentum swung to Williams and victory appeared a formality after she won nine games out of 10 and set up a match point.
But the momentum then swung back again to Pliskova in a chaotic encounter.
"I was almost in the locker room but now stand here as the winner," she said.
"My mind was in the locker room at 5-1 down but I was still here. I was too passive and mentally down but she got a little bit shaky.
"Naomi Osaka is dangerous but there is nobody more dangerous than Serena."