Roger Federer and Serena Williams, stress-free and loving the limelight, strolled into the third round of the US Open on Thursday as the pressure began to mount at the season's last Grand Slam.

For Federer and Williams, it was business as usual at Flushing Meadows but not for Italy's Sara Errani, the women's fourth seed.

Crumbling under the weight of expectation, Errani crashed to a 6-3 6-1 loss to compatriot Flavia Pennetta, then made the startling admission she choked under pressure.

Federer, unflappable even as he struggles to add to his record collection of 17 Grand Slam singles titles, hardly raised a sweat as he brushed aside Argentina's Carlos Berlocq 6-3 6-2 6-1.

"For me it was pretty straightforward, to be honest," Federer said. "It's one of those matches I expect myself to win if possible in straight sets and gain confidence in the process.

"All those things happened, so, yeah, I'm pleased about it."

Williams was also unflustered even though the wind was blowing hard when she strolled on to the Arthur Ashe Stadium center court.

Her match against Galina Voskoboeva of Kazakhstan had originally been scheduled for Wednesday but was held over because of rain. Unfazed, she cruised to a 6-3 6-0 win.

"I'm just trying to do the best I can," Williams said. "Just always trying to get a little better."