World no.1 Caroline Wozniacki and her chief rankings rival Petra Kvitova had demanding three-set introductions to the Sydney International in their first official matches of the season yesterday.

Wozniacki and Kvitova, tuning up for next week’s Australian Open, were on court for more than two hours in warm conditions after beginning their Australian campaigns indoors at last week’s Hopman Cup in Perth.

Wozniacki was beaten by Kvitova in three sets in the mixed teams Hopman Cup, after beating Bethanie Mattek-Sands and Tsvetana Pironkova in her other singles matches.

After her two hour and 22 minute match against the 18th-ranked Slovakian Dominika Cibulkova, the Dane said her 7-5, 2-6, 6-4 victory had been a tough contest.

“I thought I didn’t have that chance, but I never gave up the fight,” said Wozniacki, whose tenure at the top of the women’s singles rankings comes despite not yet winning a grand slam in 19 attempts.

Wozniacki set up a quarter-final clash against Poland’s Agnieszka Radwanska, who overcame Germany’s Andrea Petkovic in straight sets. Wozniacki leads Radwanska 5-1.

Kvitova trails Wozniacki by 295 rankings points with 470 points up for grabs to the winner of the Sydney International.

She also had a tough fight against Romania’s Alexandra Dulgheru, needing two hours and 18 minutes to defeat the world no.66 at the Ken Rosewall Arena.

The powerful left-hander faltered in the heat during the middle set before regaining her form and setting up a quarter-final with Daniela Hantuchova.

Defending champion Li Na also had a difficult time before subduing South African Chanelle Scheepers 2-6, 6-4, 6-1 to set up a quarter-final with Lucie Safarova.

Venus out

Seven-time Grand Slam singles champion Venus Williams withdrew from the Australian Open as she struggles to return from the autoimmune disease Sjogren’s syndrome.

In a posting on her website, the US player said that she has been making progress and plans to return to WTA Tour play in February, when events begin in the United States.