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.
Czech Kvitova will meet either top seed Ash Barty or Alison Riske, who play later on Sunday, in the last eight.
