Ash Barty out of Australian Open following upset three-set loss to Karolína Muchová

The second-set injury timeout for Karolína Muchová appeared to unsettle Ash Barty.(AAP: Dave Hunt)

World number one Ash Barty has made a shock exit from the Australian Open after losing her quarter-final to Karolína Muchová 1-6, 6-3, 6-2 on Rod Laver Arena.

Barty appeared headed for a convincing win when she won the first set 6-1 in just 24 minutes, and led 2-1 with a service break up her sleeve in the second.

Play was halted at this point when Muchová left the court for treatment and a medical timeout, and the course of the match changed dramatically once the second set resumed.

Muchová won five of the next six games to claim the second set, before gaining an early service break in the third as Barty struggled to regain her focus.

The Australian was broken again in the seventh game of the third set, allowing the Czech 25th seed to serve out the match to book a berth in the semi-finals of a major for the first time in her career.

Muchová will face the winner of the all-American encounter between Jennifer Brady and Jessica Pegula in the last four.

She acknowledged after the match that the medical timeout was the turning point of the match.

“I start to feeling a bit lost by the end of the first set, she played almost like [she was making] no mistakes,” Muchová said in her on-court interview.

“I tried to get back, played a bit faster rallies so we don’t play the long ones as in the first set and it worked well.”

What went wrong with Barty’s game in the second set and beyond will be analysed in detail for some time.

She had only made six unforced errors in the first set, but that figure crept up to 37 by the end of the match.

Barty dropped serve four times after Muchová returned from her medical timeout and failed to break her opponent again.

Earlier, the Australian, hoping to become the first local to win the women’s singles title in 43 years, could not have asked for a better start to the contest.

She got a service break in the second game of the match to lead 2-0, with three clean forehand winners from the baseline helping to put Muchová on the back foot early in the contest.

The Australian was barely challenged during her service games in the first set and with another break of the Muchová serve she jumped out to a 5-0 lead.

It was a case of third time lucky for Muchová when she held in the sixth game to trail 1-5.

But it was not enough to halt Barty’s momentum and the top seed claimed the first set in 24 minutes.

Barty reinforced her command of the match early in the second set, breaking Muchová and holding to lead 2-0.

Muchová left the court for treatment after holding serve in the third game, with the pause in play being extended while she took the medical timeout.

The halt to proceedings seemed to provide Muchová with a much-needed circuit breaker, as she broke Barty’s serve for the first time in the match once play resumed.

She won her next service game and had a break point at 3-2, however Barty served her way out of trouble to level the second set.

Muchová, who lost her only previous match against Barty at the 2018 US Open, survived two break points before winning the seventh game.

The second break point saved by Muchová followed a remarkable rally.

She forced Barty to play defensively from beyond the baseline with several backhand lobs while being peppered with overhead smashes.

Barty dropped her next service game to trail 3-5, before Muchová comfortably served out the set to force a deciding third.

Muchová, brimming with confidence, marched on and served for the match at 5-2, although Barty was refusing to give up.

She had several break points, but Muchová settled and closed out her victory in one hour and 57 minutes.

ABC