Former champion Serena Will-iams stepped up her game to beat Wimbledon runner-up Marion Bartoli 6-3, 6-4 to reach the quarterfinal of the US Open on Sunday.

The eighth-seeded American recovered from an early break down and went on to dominate from the baseline to win in 76 minutes. She set up a possible clash with top seed Justine Henin.

Australian Open champion Williams had struggled in her first three matches and looked set for another tough battle against the 10th-seeded Frenchwoman when she fell 2-0 down early on.

But the American found her range quickly, served well throughout and was rarely troubled as she clinched a comfortable victory.

Also on Sunday, in an upset of sorts, Argentine Juan Ignacio Chela won through to the men’s fourth round. Chela, the 20th seed, came from two sets to one down to send 12th-seeded Ivan Ljubicic of Croatia packing, pulling off a 6-4, 6-7 (5-7), 2-6, 6-3, 6-3 victory.

Joing Chela in the round of sixteen was Spaniard David Ferrer. The 15th seed outlasted 24th-seeded Argentine David Nalbandian 6-3, 3-6, 4-7, 7-6 (7-5), 7-5 in a match that went the distance and had the Louis Armstrong stadium court enthralled.

Federer stretched

On Saturday, Roger Federer, aiming for a fourth consecutive US Open title, defeated hard-hitting rookie John Isner 6-7, 6-2, 6-4, 6-2 in a men’s third-round encounter.

Federer had only 11 unforced errors against the American wildcard, who has been impressive since joining the tour in July.

“It's so hard to play against players like him, you just hope he's not going to keep serving aces,” said Federer, who watched nine of Isner's 18 aces fly by in the opening frame.

“It was unbelievable how he served in the first set. But I started to get a read of it a bit in the second and third.”
Russian fourth seed Nikolay Davydenko reach-ed the fourth round with a 7-5, 6-0, 7-5 victory over Spaniard Nicolas Almagro, while number five and 2003 champion Andy Roddick blasted 19 aces to defeat Sweden's Thomas Johansson 6-2, 6-2, 6-0.

Sixth-seeded American James Blake also advanced beating Austrian Stefan Koubek 6-4, 3-6, 7-6, 6-1.
On the women's side, number seven seed Nadia Petrova of Russia committed 29 errors during a 6-4, 6-4 upset loss to 18-year-old Hungarian Agnes Szavay.

Fourth-seeded former champion Svetlana Kuznetsova kept Russian hopes alive, beating Spain's Anabel Medina Garrigues 6-3, 6-1.

Exit Hingis

Martina Hingis' 10-year anniversary since winning the US Open ended in disappointment when she lost to Belarussian Victoria Azar-enka 3-6, 6-1, 6-0.

Another favourite to fall was 13th seed Nicole Vaidisova of Czech Republic, a 6-4, 3-6, 7-6 loser to Israeli Shahar Peer in the first women's match of the tournament to be decided in a third-set tie-breaker.

Mahesh-Sania win

Mahesh Bhupathi and Sania Mirza reached the quarterfinals of mixed doubles with a 7-6 (7-4), 3-6, 10-2 win over Tatiana Golovin of Fr-ance and Bob Bryan.

In another match, Leander Paes, teaming up with Meghann Shaughnessy of US, beat fifth-seeded Martin Damm and Kveta Peschke of the Czech Republic 7-5, 6-3 to also enter the last eight stage.