It was a positive start to the year for world No. 1 Caroline Wozniacki, who came back from 4-0 down in the third set to defeat Dominika Cibulkova in the second round of the Sydney International.

33393 - Wozniacki in dramatic comeback to reach quarters

Wozniacki was given a bye in the first round, and showed signs her game is not yet at its peak as Cibulkova pushed the Dane to three sets. Wozniacki ultimately prevailed 7-5 2-6 6-4, winning the final six games of the match to progress to the quarter-finals.

The 21-year-old was aided by Cibulkova dishing up 10 double faults in the contest, while six aces also helped Wozniacki to hold serve at vital moments. Wozniacki will now take on seventh seed Agnieszka Radwanska who defeated Germany's Andrea Petkovic 7-5 6-4.

"She was hammering the ball. I was just standing there and trying to figure out what to do," Wozniacki said. "I felt like everything I tried to do wasn't working and I was making a lot of unforced errors. So I said, 'Okay, let's just keep a margin to the lines and give her that extra ball.' It paid off in the end.

"That I could fight back from that score and win is definitely satisfying, but I'll need to step my game up a little bit in the next round."

Wozniacki could lose her No. 1 ranking if Wimbledon champion Petra Kvitova wins the title in Sydney this week, but the Czech also needed three sets to battle her way past Alexandra Dulgheru. The No. 2 seed grabbed an early break in the third set to claim a 7-5 3-6 6-4 victory and avenge her US Open defeat to the Romanian.

"It was my first match of the tournament and first match outdoors. It was hard getting used to the conditions," Kvitova said. "Usually when I go outdoors, the serve is the biggest problem for me, but today it was really good. And it was a little bit in my head that I lost to her at the US Open - it was a tough first match for me here, but I really wanted to win against her today."

Defending champion Li Na also moved on to the quarters as she recorded a 2-6 6-4 6-1 triumph over Chanelle Scheepers. It was particularly slow start by the Chinese, who managed to win just seven points on serve in the opening set before returning to form in the second. Na will face Daniela Hantuchova next after the Slovakian ousted Francesca Schiavone in straight sets.

Meanwhile, Svetlana Kuznetsova is the latest injury doubt ahead of next week's Australian Open. The Russian retired injured while 6-2 2-0 down against Lucie Safarova.

Elsewhere, at the Hobart International, top seed Yanina Wickmayer crushed Casey Dellacqua 6-1 6-1 to reach the quarter-finals, where she will meet Simona Halep who won an all-Romanian encounter against eighth seed Irina-Camelia Begu 6-4 6-2.

Fourth seed Angelique Kerber won through to the quarter-finals with a 6-1 6-2 thrashing of Sara Errani, while Sorana Cirstea joined compatriot Halep in the last eight after she came from behind to beat American Bethanie Mattek-Sands 2-6 6-3 7-5.