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SISTER ACT is on song in oz open

Defending champion Serena Williams unleashed a barrage of winners to end local hopeful Sam Stosur's campaign at the Australian Open today.

Williams, yet to drop a set so far in Melbourne this year, silenced a near-capacity crowd at the Rod Laver Arena with 42 winners to claim a 6-4 6-2 victory in just over an hour.

Such was Williams' dominance she conceded just two points on her serve in the first set as 13th seed Stosur, who had beaten the 11-time grand slam winner in their previous meeting, was completely outgunned.

"I can't believe it. Sam beat me last time convincingly," Williams said. "I think my serve was pretty good today. I had to come out strong because when you are playing someone like Sam you have to play this good.

"I especially had to do that in front of this crowd or I would have been going home."

It was a good day for the Williams as Serena's sister, Venus, continued her domination of Francesca Schiavone, coming back from a set down to defeat the Italian 3-6 6-2 6-1 and reach the last eight as well.

Seventeenth seed Schiavone, who had never beaten Williams in five previous matches, looked set to break the trend after taking the first set and an early break in the second.

Williams broke back immediately to steal the momentum, however, and then steamrolled the Italian in the last set with confident net play. The American now plays China's Li Na in the quarter-finals after the 16th seed upset world No4 Caroline Wozniacki 6-4 6-3.

It was not an upset of major proportions, but it was still a surprise as Wozniacki made the final of last year's US Open and was seeded fourth at Melbourne Park.

Williams and Li have played each other just once previously, at the Beijing Olympics where the Chinese triumphed 7-5 7-5 in the quarter-finals.

Third men's seed Novak Djokovic eased to another routine win at the Australian Open to reach the quarter-finals. The 2008 winner needed less than two hours to claim a 6-1 6-2 7-5 win over the world No86 Lukasz Kubot.

Djokovic's win followed his 6-1 6-1 6-2 demolition of Denis Istomin in the previous round as the Serb's untroubled run into the latter stages of the tournament continued.

The 22-year-old has dropped just one set, against Marco Chiudinelli in the second round.

Kubot became the first Polish player to reach the fourth round of a grand slam since Wotjek Fibak at Roland Garros in 1982 after Mikhail Youzhny pulled out on the eve of their third round match due to a wrist injury.

The 27-year-old could not make the most of his fortune though as he was easily brushed aside by Djokovic. The Serbian broke his rival twice in the opening set before clinching it with an ace in 28 minutes. The second set did not take long either with Djokovic wrapping it up in 33 minutes before Kubot at least provided some resistance.

The Pole was level at 5-5 in the third set but disappointingly handed Djokovic the break with a double fault. The Serb served the match out completing a comfortable day with a forehand winner.

Nikolay Davydenko continued his run with a tense 6-2 7-5 4-6 6-7 6-3 fourth round victory over ninth seed Fernando Verdasco. The Russian sixth seed, the form player on the men's tour over the past six months, had not lost a set coming into the match but the Spaniard showed in the third and fourth sets that he was vulnerable.