Estonia's Kaia Kanepi rallied from a set down to topple world number two Aryna Sabalenka 5-7 6-2 7-6(10) on Margaret Court Arena in a tight contest on Monday to reach the Australian Open quarter-finals for the first time.
Having surrendered the opening set for three matches in a row, Sabalenka took a one-set lead for the first time in Melbourne but was unable to build on it as her serving issues resurfaced once again.
The Belarusian committed 15 double faults in another error-strewn performance, five more than she had in her third-round win over Marketa Vondrousova.
Kanepi was gifted a double break early in the second set with back-to-back double faults from her 23-year-old opponent and did not waste the opportunity as she cruised to a 4-0 lead before taking the set.
The 36-year-old carried that momentum into the decider and looked set to go 5-3 up but Sabalenka saved four break points to hold for 3-4 and level it, before suffering a service meltdown again and hitting three double faults in four points.
Kanepi was made to work for her victory after being unable to close the match from 40-0 up as Sabalenka saved four matchpoints to break back, before the pair traded holds to take the deciding set into a tiebreaker.
{{/usCountry}}Kanepi was made to work for her victory after being unable to close the match from 40-0 up as Sabalenka saved four matchpoints to break back, before the pair traded holds to take the deciding set into a tiebreaker.
{{/usCountry}}The Estonian finally prevailed in the tiebreak, taking advantage of a string of unforced errors from Sabalenka to convert her fifth matchpoint and complete the upset.
"I think I would be more happy if I won after two, three matchpoints," Kanepi told reporters. "It was really close, I almost lost the match.
"My hand was shaking when I started serving in that game. I didn't make any first serves in, and that added to the pressure.
"I almost didn't (recover). I guess I was just lucky at the end. So close."
Sabalenka expressed disappointment in her performance but said there were still positives to take from the defeat.
"I had all the opportunities and I didn't use it," Sabalenka said. "I would say I started well but I lost focus and it became really emotional. I couldn't find a way back.
"Compared to the beginning of the season, I'm really happy that I was able to kind of find the rhythm on my serve. So there is still something positive."
Kanepi will take on 2020 French Open champion Iga Swiatek, who beat Sorana Cirstea 5-7 6-3 6-3 earlier on Monday, for a place in the semi-finals.
The world number 115 has reached the quarter-finals of a Grand Slam on six previous occasions, most recently in the 2017 U.S. Open, but has never managed to progress beyond the last eight.