NEW YORK -- Only a few spots separate them in the seedings. Still, the considerable gulf between No. 1 Serena Williams and No. 4 Sara Errani was hard to ignore in their back-to-back matches Thursday at the U.S. Open.

Williams, seeking her 17th Grand Slam title and second straight at Flushing Meadows, brushed off an ungainly slide onto 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, but it was OK," she said.

Only an hour before on the same court, a much different scene: Errani imploded in a 6-3, 6-1 loss to her Italian teammate, 83rd-ranked Flavia Pennetta. Then, with tears welling 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. I've lost a million times in my life," 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 U.S. Open, where the tournament got back on track after a rainy Wednesday that postponed eight women's matches and shuffled the lineups.

Among the results from Thursday's full slate:

  • No. 2 Rafael Nadal improved to 17-0 on hard courts this season with a 6-2, 6-1, 6-0 victory over qualifier Rogerio Dutra Silva.

  • No. 4 seed David Ferrer overcame an error-filled second-set tiebreaker to top Roberto Bautista Agut 6-3, 6-7 (5), 6-1, 6-2.

  • Second-seeded Victoria Azarenka defeated Aleksandra Wozniak of Canada 6-3, 6-1.

  • Sixth-seeded Caroline Wozniacki beat Chanelle Scheepers 6-1, 6-2 to open the night session.

    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. 13 seed John Isner, the highest-ranked American man, defeated 39th-ranked Gael Monfils of France 7-5, 6-2, 4-6, 7-6 (4).

    American James Blake, who announced Monday that the U.S. Open would be his final tournament, lost in doubles to close out his career. Blake, already eliminated in singles, and fellow American Jack Sock fell 4-6, 6-2, 6-2 in the opening round in doubles to second-seeded Bruno Soares and Alexander Peya.