World number one Caroline Wozniacki and former champion Maria Kirilenko both reached last eight at the China Open on Thursday but followed different paths.

Defending champion Wozniacki of Denmark scored a gritty victory over Kaia Kanepi from Estonia at 6-3, 7-6(3) while the 2005 China Open champion Kirilenko of Russia was on the rise by beating Tamira Paszek of Austria 6-1, 6-2.

Wozniacki's defending campaign looked much easier when world number four Victoria Azarenka of Belarus pulled out of the Premier-level tournament where she has reached the last 16.

The China Open, which ran in its eighth year, has lost world number one Novak Djokovic, Maria Sharapova and the Williams sisters to injury or weird illness prior to the opening.

The draw became specially clear-cut after reigning Grand Slam winners Li Na of China (French Open), Petra Kvitova of Czech Republic (Wimbledon) and Australian Samantha Stosur (U.S. Open) were all shocked in first two rounds.

Azarenka's pull-out will benefit the 13th seed Anastasia Pavlyuchenkova of Russia, who trailed 3-0 in lifetime against her Belarusian nemesis.

Next up in the quarterfinals for the 20-year-old Russian will be Germany's ninth seed Andrea Petkovic.

Wozniacki's match was played in a roller coaster pattern. Wozniacki took the opening set routinely after taking one break in Kanepi's serve,but the Estonian's confidence looked unaffacted in the second set.

The players exchanged break two times until the tiebreak where the Dane held her nerve to take it at 6-3.

Wozniacki, the only top 10 player left in the draw after Azarenka's withdrawal, shall face Italian Flavia Pennetta, who defeated Dominika Cibulkova of Slovakia 6-1, 4-6, 6-4 in the quarterfinals.

Kirilenko, who sent U.S. Open winner Stosur crashing out of the tournament, looked to be at about her peak of the hardcourt game in the clash against Paszek.

It was a particularly strong serving day for Kirilenko, who lost just 15 points in eight service games - she also broke Paszek twice in each set.

Kirilenko will take on Romanian Monica Niculescu, who came through a worrying first set to outclass Frenchwoman Virginie Razzano in the all-qualifier battle 4-6, 6-1, 6-2.

Niculescu, who had beaten No.4 seed and French Open champion Li Na earlier in the week, lost a marathon 62-minute first set but came roaring back in the second and third sets, using her unique mix of paces and spins to cruise past Razzano.

Fresh off her second Premier title of the year in Tokyo, 11th seed Agnieszka Radwanska put up a below-bar performance in the third round match against Sofia Arvidsson, but it's enough to beat the Swede 6-4, 6-2 in a shade over one hour.

Both players had trouble in serving, with Radwanska dropping four service games while Arvidsson at three in the first set. With one break up, the 22-year-old Pole took the first set at 6-4.

The 2009 China Open runner-up looked a lot more convincing in the second set and revived some of her pinpoint baseline hitting, but she still capitulated in two of her games.

By breaking back four times, the Pole racked up the scratchy victory, which set up a mouthwatering quarterfinal against former world number one Ana Ivanovic, another in-form player who ousted third seed Vera Zvonareva in previous day.

In men's part, former top ten player Marin Cilic of Croatia defeated Italian Fabil Fognini 6-2, 6-7(1), 6-3. The 23-year-old Croat will in the quarterfinals take on South African Kevin Anderson, who battled in two tiebreaks to overcome Spaniard Albert Montanes 7-6(3), 7-6(4).

Earlier in the day, top seed Jo-Wilfried Tsonga of France made short work of Chinese wild card Zhang Ze 6-3, 6-4 for the quarterfinals where he booked a date against former world number one Juan Carlos Ferrero of Spain, who defeated compatriot Marcel Granollers 6-4, 6-4.