Petra Kvitova remains in contention for the Australian Open title and world number one ranking after beating Ana Ivanovic to reach the quarter-finals.
The Czech second seed, who has a chance of replacing Caroline Wozniacki at the top of the rankings, won 6-2 7-6 (7-2) on a scorching day at Melbourne Park.
"It was a really tough match at the end of the second set," said the reigning Wimbledon champion.
Kvitova will play Sara Errani of Italy, who beat China's Zheng Jie 6-2 6-1.
I'm lucky I played at 11 o'clock so wasn't too bad, but it's nice to have it warm and it's Australia so we're prepared for thisPetra Kvitova
"I missed an easy shot and lost eight points in a row, but I played well in the tie-break," Kvitova added.
"I'm lucky I played at 11 o'clock so wasn't too bad, but it's nice to have it warm and it's Australia so we're prepared for this."
Ivanovic was expected to give Kvitova her toughest test of the tournament so far, but was quite comfortably dispatched.
Both players confidently negotiated their opening service games but Ivanovic faltered in game three as a double-fault and backhand into the net gifted her opponent an early break.
Completely untroubled on her own delivery, Kvitova struck again in game seven before serving out the 32-minute first set.
She had to save two break points early in the second and then broke for 3-2 when Ivanovic netted a backhand.
Kvitova crumbled when serving for the match at 5-4, missing an easy smash as Ivanovic took two straight games to love.
A tie-break beckoned but it was Ivanovic who capitulated this time as Kvitova sealed a straight-sets victory.
