Seventh seed Petra Kvitova battled from a set down to defeat Greek Maria Sakkari 6-7 (4-7) 6-3 6-2 and reach the Australian Open quarter-finals.

The pair struggled with their service games in a contest where there were 12 breaks and 28 chances to do so.

After trailing by a set and a break, Kvitova broke herself in the seventh and ninth games to take the second set.

The 22nd seed's level dropped further in the third as the Czech 2019 finalist sealed victory with another break.

Kvitova will now face either world number one Ashleigh Barty or American Alison Riske in Melbourne.

"I don't know how I found my game," she said when asked about her fightback. "I just kept playing. I knew it would be a difficult match."