Top seed Ashleigh Barty upset by Muchova in Australian Open quarters

It was the first two sets Barty has dropped during the tournament, which an Australian hasn't won at Melbourne Park since John Newcombe in 1978. She was upset Wednesday by Karolina Muchova, 1-6, 6-3, 6-2.

Australia's world No.1 capitulated from a set and a service break up in a shock 1-6 6-3 6-2 quarter-final loss to Czech Karolina Muchova today.

Barty, who hadn't dropped a set on her way into the quarterfinals, started strongly against her lower-ranked opponent, but fell in three sets, 1-6, 6-3, 6-2 on Rod Laver Arena.

"I tried to get back, played a bit faster rally so we don't play that long ones [like] in the first set and it worked well". Ash started very good. She played like no mistakes. "It was very tough".

Muchova played poorly at the start of her second major quarterfinal, and Barty raced to a 5-0 lead while losing only six points.

World number three Naomi Osaka will take on USA superstar Serena Williams in the first semi-final on Thursday to book the first spot in Saturday night's final.

Muchova told the host broadcaster after the match that while she didn't take the medical timeout for a physical issue, she did feel "lost" and needed to clear her head.

In other quarter final action on Wednesday, Andrey Rublev faces fellow Russian Daniil Medvedev while in the night session, world number two Rafael Nadal is up against Stefanos Tsitsipas. Medical personnel took her pulse and temperature before she left the court, and when the Czech returned, she played much better.

Asked if she was injured, the 2019 Wimbledon quarter-finalist said: "No". It was more they just checked my pressure because, like I said, I was a bit lost.

"They cooled me down a bit with ice and it helped me", Muchova said.

Her come-from-behind win ended top seed Barty's hopes of becoming the first home victor at the Australian Open in 43 years after Chris O'Neil's breakthrough in 1978.

Barely missing a ball as Barty's unforced error tally mounted, Muchova broke the Queenslander twice more in the deciding set before converting her first match point with an ace after an hour and 57 minutes.