Top-ranked Caroline Wozniacki came back from 4-0 down in the final set to beat Dominika Cibulkova of Slovakia 7-5, 2-6, 6-4 Tuesday and advance to the quarterfinals at the Sydney International.
The match ended on a line call that was ruled in and later, on video review, shown to be out by a few millimeters, giving Wozniacki victory on her second match point.
Wozniacki, who was No. 1 for all but one week of last year, has achieved the top ranking without having won a Grand Slam. The Danish player's best finish in four appearances at the Australian Open, which begins next Monday, was the semifinals last year.
''I thought I had lost the match,'' Wozniacki said of her big third-set deficit Tuesday. ''I decided to play free, not care about the score anymore, and it worked out. I hate losing.''
Wimbledon champion Petra Kvitova, ranked No. 2 and in position to overtake Wozniacki for the top spot with a win at Sydney, also struggled against an unseeded opponent before advancing to the quarterfinals with a 7-5, 3-6, 6-4 win over Alexandre Dulgheru of Romania.
Kvitova used a strong serve to set up an easy cross-court forehand at the net to the open corner for the win on her first match point.
''I lost against her (Dulgheru) in the U.S. Open, so it was a little bit in my head, and I wanted to win,'' Kvitova said.
In other second-round matches, third-seeded Victoria Azarenka of Belarus beat Jelena Jankovic of Serbia 6-4, 6-2, French Open champion Li Na beat Channelle Scheepers of South Africa 2-6, 6-4, 6-1, and seventh-seeded Agnieszka Radwanska of Poland defeated Andrea Petkovic of Germany 7-5, 6-4.
Daniela Hantuchova of Slovakia, beaten by Kaia Kanepi of Estonia in the Brisbane International final last Saturday, defeated 2010 French Open champion Francesca Schiavone of Italy 7-5, 6-1. On Monday, Schiavone beat U.S. Open winner Samantha Stosur of Australia in the first round.
Former U.S. Open champion Svetlana Kuznetsova withdrew from her match against Lucie Safarova while down 6-1, 2-0, citing heat illness.
In men's matches, fifth-seeded Viktor Troicki of Serbia beat former No. 1 Lleyton Hewitt of Australia 4-6, 6-3, 6-2 and eighth-seeded Radek Stepanek of the Czech Republic defeated Xavier Malisse of Belgium 6-7 (4), 6-4, 6-4.
Julien Benneteau of France beat Italian Andreas Seppi 6-3, 6-4 and former Australian Open finalist Marcos Baghdatis of Cyprus defeated Russian Dmitry Tursunov 6-4, 6-4.
