Serena Williams powered her way into the US Open third round with a quickfire victory over Hungary's Melinda Czink.

World number two Williams, bidding for a fourth US Open title and 12th grand slam of her career, took just 53 minutes to use her renowned heavy hitting and blast her way past the hapless Czink 6-1 6-1 under the lights at Arthur Ashe Stadium.

Williams, also the reigning Australian Open and Wimbledon champion, was in complete control against the Hungarian, not allowing the underdog a single break point throughout the match, committing only nine unforced errors and winning the match on a double fault from Czink that summed up the helplessness of the challenger.

Williams, who will next play Maria Jose Martinez Sanchez of Spain in round three, was in understandably buoyant mood following her effortless victory, dancing on court as she milked the crowd's applause.

"I think I kept my unforced errors low tonight," Williams said as she pinpointed her biggest plus point from the win against a woman she had played at the end of July on a hard court and had won on a second-set tie-break.

"I definitely made some adjustments," she said. "I played her a few weeks ago for the first time so I knew her game better today. She's a really good player so I was really pumped coming out here and I knew I had to play really good."

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In the other quarter of Serena's half of the draw, former champions Kim Clijsters and the champion's sister Venus stayed on course for a last-16 showdown at Flushing Meadows after both coming through their US Open second round ties on Wednesday.

Third seed Williams, the 2000 and 2001 champion, overcame a troublesome left knee to book her place in the third round with a battling straight-sets win over fellow American Bethanie Mattek-Sands.

Belgium's Clijsters, playing for the first time in New York since winning the women's singles title in 2005, having retired to start a family the following year, continued to show she is a dangerous wild card entry as she knocked out 14th seed Marion Bartoli of France.

Williams had needed three sets to get past first-round opponent Vera Dushevina of Russia on Monday night as she struggled for form and was restricted by her knee, which has caused her problems recently due to tendinitis.

Williams had a more comfortable afternoon at Arthur Ashe Stadium, playing with a well-strapped left knee as she saw off the world number 124, 6-4 6-2 in 91 minutes.

Mattek-Sands was never entirely out of the contest, particularly in the opening set as she forced three break points against the powerful Williams serve but the third seed's class ultimately told.

Mattek-Sands made one last stand as Williams attempted to serve out for the match, forcing the seven-time grand slam winner to save three break points - the last of those with a brilliant backhand winner at the net - before sealing victory with a blistering serve that Mattek-Sands could only divert into the stands.

Williams, who will next play world number 46 Magdalena Rybarikova of Slovakia, a three-set winner over Chang Kai-Chen of Chinese Taipei, was pleased to have bought herself extra time to get her knee in order.

Reticent about talking of her fitness problems in specifics, Williams said she would do everything she could to fight off the pain and advance through the tournament.

"I love playing this event and I'm going to do my best to win every round," Williams said.

"Wear and tear puts a lot on your body. It's September now and I started in December so I guess it's not a surprise that at this time of year things start to get a little sore and start to hurt.

"But, you know, I'm very determined to still play my best tennis in spite of everything."

Williams may well need to be on top form if she is to get past Clijsters in their potential fourth-round meeting.

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The Belgian former world number one went a set down against Bartoli and then cruised to victory 5-7 6-1 6-2 at Louis Armstrong Stadium, the second time in a month she has beaten the Frenchwoman since returning to competitive action in August.

Clijsters next faces fellow Belgian Kirsten Flipkens, who herself provided an upset when she blew away 20th seed Anabel Medina Garrigues of Spain 6-1 6-3.

There were still more seeds making early exits from the women's draw on Wednesday as number 12 Agnieszka Radwanska of Poland fell prey to Russia's Maria Kirilenko, ranked 59 in the world, losing 6-4 2-6 6-4.

Also out was France's Amelie Mauresmo, the 17th seed, beaten soundly by Canada's world number 39 Aleksandra Wozniak, 6-4 6-0, having been 4-3 up in the opening set.

Order had been maintained on the Grandstand court where both seventh seed Vera Zvonereva and eight seed Victoria Azarenka progressed.

Zvonereva scored a 3-6 6-1 6-1 win over fellow Russian Anna Chakvetadze while Azarenka of Belarus saw off Czech woman Barbora Zahlavova Strycova 6-2 6-1.

But then Australian Samantha Stosur took to the court and the 15th seed was knocked out 7-5 6-4 by American wild card Vania King.

Italy's Flavia Pennetta, seeded 10th, needed just 50 minutes to record the first "double bagel" of the tournament, beating India's Sania Mirza 6-0 6-0 on Louis Armstrong.

China's Na Li, seeded 18, ended Portuguese teenager Michelle Larcher De Brito's New York adventure with a 6-1 6-3 win over the 16-year-old, while there were also straight-sets wins for number 26 Francesca Schiavone of Italy, over Switzerland's Stefanie Voegele, and 31st seed Elena Vesnina of Russia, who beat American Jill Craybas.

In a late-starting match on Court 11, number 22 seed Daniela Hantuchova of Slovakia came from a set down against Switzerland's Timea Bacsinszky to win 5-7 6-2 6-1.