Top-seeded Russians Nikolay Davydenko and Svetlana Kuznetsova booked their quarterfinal berths on Wednesday at the Pilot Pen hardcourt tournament, last tune-up for the US Open.

Davydenko, who heads the men's field, defeated France's Fabrice Santoro 7-5, 6-3 to advance.

In the quarters he'll face sixth-seeded American Sam Querrey, who downed Germany's Bjorn Phau 7-5, 6-3.

Querrey also claimed the US Open series crown rewarding his performance in a series of tournaments throughout the year.

With his win on Wednesday, Querrey matched the 145 points of world number two Andy Murray, but he earned the title over the Scot because he won a total of 14 matches to Murray's eight.

The title gives Querrey a chance to earn a bonus of between $15 000 and $1-million, depending on his finish at the US Open.

French Open champion Kuznetsova clawed her way past Belgian teenager Yanina Wickmayer 6-4, 5-7, 7-6 (7/2).

Defending women's champion and second seed Caroline Wozniacki also advanced to the quarterfinals, defeating rising Russian Anastasia Pavlyuchenkova 6-1, 6-4.

Kuznetsova, who won two years ago, will play eighth-seeded Amelie Mauresmo of France in the quarterfinals on Thursday.

Kuznetsova admitted she lost focus at times, and said she knows she'll need to do better if she wants a shot at another Grand Slam title in New York.

"I still have it, so I appreciate that I have it, but I have to work on closing out things when I have the chance to," she said.

Wickmayer earned a break in the third set to give herself a chance to serve for the match, but Kuznetsova broke her back and went on to force the tiebreaker.

"I knew at five-all that if I wanted to win the match, I would have to play perfect," Wickmayer said. "And I almost played perfectly, but I guess in the tiebreaker she was just too good for me."

Denmark's Wozniacki will play unseeded Frenchwoman Virginie Razzano, who advanced when fifth-seeded Agnieszka Radwanska of Poland retired. Radwanska won the first set 6-3 but had dropped the second 6-4 when she retired with a hand injury.

French sixth seed Marion Bartoli retired while trailing in the third set against Slovakian qualifier Magdalena Rybarikova, who had dropped the first set but held on and was leading 1-6, 7-6 (7/5), 2-0 when Bartoli retired with a strained left thigh.

WTA Tour officials said Bartoli was expected to be able to play in the US Open, which starts Monday at Flushing Meadows.

Rybarikova will face third-seeded Italian Flavia Pennetta fired eight aces in a 7-6 (7/1), 6-4 victory over Czec Iveta Benesova.

"My serve helped me a lot on the important points. I didn't make a lot of mistakes and I was very aggressive," said Pennetta, who will take on

Unseeded Russian Elena Vesnina advanced, rallying for a 3-6, 6-3, 6-4 victory over Aussie Samantha Stosur that set up a quarterfinal clash with Russian Anna Chakvetadze.

In other men's action, second seeded Spaniard Fernando Verdasco also advanced, shrugging off two second-set rain delays to post a 7-6 (7/3), 6-2 victory over Andreas Seppi.

"I was just giving my 100 percent to try to finish the match as soon as possible. I really played good those last three games," said Verdasco, who will play Austrian Jurgen Melzer, a 7-6 (7/5), 4-6, 6-1 winner over eighth-seeded Romanian Victor Hanescu.

Seventh-seeded Russian Igor Andreev beat Portuguese qualifier Frederico Gil 6-4, 6-4 to line up a clash with Argentina's Leonardo Mayer, who beat Italian Simone Bolelli 6-2, 6-4.

Argentina's Jose Acasuso beat Russian Igor Kunitsyn 3-6, 7-6 (7/3), 6-3 and will play France's Florent Serra, a 4-6, 7-6 (8/6), 7-5 winner over American wild card Rajeev Ram.