NEW YORK — Rafael Nadal encountered as much trouble from his own body as his opponent in a third-round victory at the U.S. Open today.

The third-seeded Nadal, who missed Wimbledon with sore knees, needed a 10-minute injury break for a trainer to work on his abdominals early in the third set of his 7-5, 6-4, 6-4 victory over No. 32 Nicolas Almagro on Sunday.

The stomach injury first cropped up for Nadal last month at a tournament in Cincinnati.

While Nadal laid on the ground to receive treatment, Almagro was laying down to get work done on his back.

The Spaniards popped back up and Nadal finished the work, staying in the hunt to complete his career Grand Slam, though it has yet to be seen what kind of toll this match took on him.

"I feel it a little bit now, but I'll try my best to recover for the next match," said Nadal, who has insisted all week that he's been feeling fine. "I'm here to work hard and try my best all the time."

Earlier, No. 2 Serena Williams routed No. 22 Daniela Hantuchova of Slovakia 6-2, 6-0, winning the final 10 games after starting the first set 2-2.

Williams has reached the quarterfinals at 11 of the past 12 major tournaments and won the title at three of the past four.

She is still seeking her first big test at Flushing Meadows.

"I just want to keep this level and just stay focused," Williams said.

In other early action Sunday, 11th-seeded Fernando Gonzalez defeated 17th-seeded Tomas Berdych, 7-5, 6-4, 6-4, and No. 9 Gilles Simon of France retired because of a knee injury while trailing No. 24 Juan Carlos Ferrero 1-6, 6-4, 7-6 (5), 1-0.

"Sometimes, I don't know why, I just feel a big pain," said Simon, who added that he's had problems with the knee since the French Open in May.

In the other early women's match, No. 18 Li Na of China ousted No. 26 Francesca Schiavone of Italy, 6-2, 6-3.

No. 3 Venus Williams had an afternoon match against unseeded Kim Clijsters, who is facing, by far, the toughest match in her first appearance at the U.S. Open since she won it in 2005.

Also later, No. 2 Andy Murray was scheduled to play 195th-ranked Taylor Dent of Newport Beach, Calif., who has won two rounds in his inspirational comeback from back surgery.