Petra Kvitova came from a set down and took full advantage as her Greek opponent Maria Sakkari's self-belief drained away to advance to the Australian Open quarter-finals with a 6-7(4) 6-3 6-2 victory on Rod Laver Arena on Sunday.
Seventh seed Kvitova looked second best early on against Sakkari, who was backed by loud support from local Greek fans, but seized the advantage in a second set where both players struggled to hold serve.
The two-times Wimbledon champion broke Sakkari four times in the second set and then took a 3-0 lead in the decider to give her the advantage she needed to put away the stubborn 22nd-seed in two hours, 12 minutes.
"It's pretty tough to play Maria. I lost the last time I played her so I knew it would be difficult," Kvitova said.
"I had to fight pretty hard ... but suddenly I got used to her game and was playing more rallies and starting to play my own game."
Later, American Sofia Kenin ended teen sensation Coco Gauff's run at the Australian Open with a 6-7(5) 6-3 6-0 victory to reach her first career Grand Slam quarter-final.
The 15-year-old Gauff, who had beaten defending champion Naomi Osaka in her previous match and seven-times Grand Slam winner Venus Williams in her opener, rallied from a break down to win the opening set in a tiebreaker.
While Gauff enjoyed most of the support at the packed Melbourne Arena, Kenin, the 14th seed, fought her way back into the match and got the crucial break in the second set when Gauff served three double faults in the fourth game.
The unforced errors kept mounting for Gauff in the third set as Kenin broke her three times to secure her place in the quarter-finals against either China's Wang Qiang or Ons Jabeur of Tunisia.
In the men's draw, in-form Canadian Milos Raonic pounded down 35 aces and 55 winners to overcome Croatian Marin Cilic 6-4 6-3 7-5 and become the first man to reach the quarter-finals.
The 29-year-old, a former world No.3, is seeded a lowly 32nd at Melbourne Park but has been in impressive form over the first week and reached the last eight without losing a set.
Cilic, the 2014 US Open champion, may have been feeling the effects of two five-set matches against seeded opponents earlier in the tournament and needed a lengthy medical timeout for treatment on his back at 3-0 down in the second set.
Also a former world number three, the 31-year-old still had enough game to test Raonic, especially when he was able to engage the Canadian in lengthier rallies.
Raonic was consistently sending down serves well in excess of 200 kilometres per hour (124 mph), however, and it was appropriate that he finished the match on Margaret Court Arena with one final booming ace.
"I'm just happy to be playing well, to be playing in this kind of atmosphere and this kind of support," said Raonic, a semi-finalist in Melbourne in 2016.
"It feels pretty damn good I've gotta say, I can't complain about it. It's been an exciting tournament for me so far and hopefully there are exciting things ahead."
Raonic will face Novak Djokovic, who beat Diego Schwartzman 6-3- 6-4 6-4 on Rod Laver Arena, in the last eight.
The Serbian has a 9-0 career record against Raonic, including a win in the quarter-finals in Melbourne in 2015.
The Montenegro-born world No.35 said he would need to be on top of his game to get past the defending champion.
"I think I'm going have to hit more ... aces," he laughed.