But it can only continue for one more match.

Venus and Serena posted identical 6-2, 6-1 victories in the third round Saturday. Another win, and they'll face each other in the quarterfinals.

Four of the top 10 women's seeds have lost, including No. 1 Ana Ivanovic. The sisters are the only two former champs still alive.

Venus opened play at Arthur Ashe Stadium by beating 27th-seeded Alona Bondarenko of Ukraine. About five hours later on the same court, Serena defeated 30th-seeded Ai Sugiyama of Japan.

The way both are playing and the way the top seeds are dropping, a repeat of their finals matchup at Wimbledon would seem quite plausible. Except for the pesky reality of being in the same part of the draw.

Serena, the No. 4 seed, has lost just 10 games in three straight-set wins. Venus, seeded seventh, has dropped 11.

"I think that definitely the Wimbledon win helped me a lot to change my mentality, to realize not every thing has to be perfect all the time," said Venus, who beat her sister in that final. "That's helped me to, if I don't have a perfect practice, I don't get really upset about the whole tournament."

Men's No. 1 seed Rafael Nadal came back from down a break in the second set to beat Viktor Troicki of Serbia 6-4, 6-3, 6-0. His next opponent will be American Sam Querrey, who reached the fourth round of a grand slam for the first time with a 7-6 (5), 7-6 (5), 6-2 victory over No. 14 seed Ivo Karlovic of Croatia.

The 20-year-old Querrey came into the year with two goals: win an ATP tournament and raise his ranking into the 30s.

He accomplished both, winning in Las Vegas in March and climbing to No. 38 in May. Currently ranked 55th, his next goal is to end the year at No. 32 or better so he'll be seeded at the Australian Open.

The 6-foot-6 Querrey is considered the tall guy with the big serve against most opponents, but not the 6-10 Karlovic. In his second-round match, Karlovic led Florent Serra in the aces department 42-0.

This time, Karlovic only edged Querrey 24-20 and struggled to win points against Querrey's serve. Karlovic managed just three break points and didn't convert any.

"If I can get my racket on the ball, it's not too bad," Querrey said of Karlovic's serve. "I'm a tall guy, as well. It's up near my shoulders, where other guys it's toward their head. ... Against a guy like him, there's a sense of urgency to every point, especially when he's serving."

Julie Coin's magical stay at the Open is over. The world's 188th-ranked women's player upset Ivanovic on Thursday, but her run ended in the third round with a 6-4, 6-4 loss to fellow Frenchwoman Amelie Mauresmo, the No. 32 seed.

Sam Querrey pulled the biggest men's upset by beating No. 14 Ivo Karlovic 7-6 (5), 7-6 (5), 6-2.

Querrey added that to his victory over No. 22 Tomas Berdych in the first round. A far tougher test follows, of course: Wimbledon, French Open and Olympic champion Rafael Nadal, who won for the 41st time in his last 42 matches by brushing aside Viktor Troicki 6-4, 6-3, 6-0.

In other third-round action Saturday, French Open semifinalist Gael Monfils, seeded 32nd here, beat No. 7 David Nalbandian in straight sets, then showed off some club-worthy dance moves to mark a victory he called "gorgeous." Monfils now meets the winner of Saturday night's later match between two Americans, No. 9 Blake and Mardy Fish.

No. 6 Andy Murray of Britain came all the way back from a two-set deficit to defeat a fading Jurgen Melzer of Austria 6-7 (5), 4-6, 7-6 (5), 6-1, 6-4. Murray celebrated by pushing up his gray T-shirt's right sleeve and flexing his biceps -- a signal to his fitness trainer and support team.

His next opponent is No. 10 Stanislas Wawrinka of Switzerland, who also dropped the first two sets before winning in five against Flavio Cipolla of Italy.

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