NEW YORK (AP):

The considerable gulf between No. 1 Serena Williams and No. 4 Sara Errani was hard to ignore in their back-to-back matches yesterday at the US Open.

Williams, seeking her 17th Grand Slam title and second straight at Flushing Meadows, brushed off an ungainly slide on to her backside en route to a typically easy second-round victory, 6-3, 6-0 over Galina Voskoboeva in half-full Arthur Ashe Stadium.

Barely worth talking about by Williams' standards: "I'll have to think about it and see what I can do better," she said, "but it was OK."

High expectations

Only an hour before on the same court, a much different scene: Errani imploded in a 6-3, 6-1 loss to fellow Italian, 83rd-ranked Flavia Pennetta. Then, while tears welled up in her eyes, Errani conceded that she's struggling to handle her high ranking and the high expectations that have come with that.

"My problem isn't that I lost," Errani said. "My problem is trying to find the desire to fight and be on the court ready to fight. For a few weeks, I haven't felt like I wanted to be on the court. That's the problem."

That concession was the most unexpected development on Day 4 of the US Open, where the tournament got back on track after a rainy Wednesday that postponed eight women's matches and shuffled the line-ups.

Williams got through her win unscathed, and when she was done in Ashe Stadium, five-time champion Roger Federer, the seventh seed, dispatched Carlos Berloq 6-3, 6-2, 6-1 in 1 hour, 35 minutes.

"It's one of those matches I expect myself to win if possible in straight sets and gain confidence in the process," Federer said. "All those things happened, so, yeah, I'm pleased about it."

No. 4 David Ferrer overcame an error-filled second-set tiebreaker to beat Roberto Bautista Agut 6-3, 6-7 (5), 6-1, 6-2, and No. 2 Rafael Nadal was playing the late match.

On the women's side, second-seeded Victoria Azarenka had no trouble in defeating Aleksandra Wozniak of Canada 6-3, 6-1 and sixth-seeded Caroline Wozniacki opened the night session with a 6-1, 6-2 win over Chanelle Scheepers.

Williams was pushed only briefly against Voskoboeva, ranked 77th from Kazakhstan.

Serving at game point trailing 5-3, Voskoboeva drew Williams to the net, and as Williams reached for the ball, her feet slid out from under her and she fell hard on to her backside, her racket slamming to the ground. Before she fell, however, she reached the shot to win the point. Two points later, she closed out the set.