Charles Krupa, Associated Press
Venus Williams returns a shot to Alona Bondarenko during the U.S. Open tennis tournament on Saturday.

NEW YORK — The Williams sisters keep cruising along while other top women's seeds go crashing out of the U.S. Open.

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.

Querrey was hardly the only man to author a surprise Saturday, capped by Mardy Fish's 6-3, 6-3, 7-6 (4) victory over No. 9 Blake in an all-American match at night. Fish took the last five points to earn his first berth in the fourth round at the U.S. Open.