Defending champion Andy Roddick was eliminated in his opening match at the Sony Ericsson Open in Key Biscayne, Florida, on Saturday.

Roddick had trouble breathing because of chest congestion and lost to Pablo Cuevas of Uruguay 4-6, 6-7 (4).

Roddick received three visits from a trainer during changeovers in the second set. He has struggled to shake a bronchial infection he contracted last month and plans to see a doctor when he returns home to Austin, Texas.

He began limping at the end of the match and said he also had an injury, but he declined to elaborate.

"I have to get some stuff looked at," he said.

Roddick played with a mild case of mononucleosis last summer, and he's wondering about the extent of his current malady.

"It's deep in the chest," he said. "It's not even so much nasally or throat or anything like that. It's just when I laugh, I start sounding like a car trying to start."

There was nothing to laugh about against Cuevas, a 25-year-old journeyman who beat a top-10 player for the first time. Roddick said the way he felt, he wasn't surprised to lose.

"I didn't feel very optimistic throughout the day," said Roddick, who won the Key Biscayne title in 2004 and 2010.

Much more robust were top seed Rafael Nadal and No. 3 Roger Federer, who easily advanced to the third round. In women's third-round play, No. 1 Caroline Wozniacki beat No. 29 Daniela Hantuchova 6-1, 7-6 (7).

Nadal, seeking his first Key Biscayne title, held every service game and beat Kei Nishikori 6-4, 6-4.

Federer beat Radek Stepanek 6-3, 6-3 for the 762nd victory of his career, tying him with Pete Sampras for seventh place in the Open era. "It's nice tying Pete, but he could have played for many more years," Federer said. "He could still win some matches on tour now if he wanted to."

Federer, who won Key Biscayne in 2005 and 2006, faced only one break point against Stepanek and has won 18 consecutive sets from the Czech. "I was able to play solid and keep him moving and serve at a high first-serve percentage," Federer said. "All in all, I'm really pleased."

Federer improved to 19-3 this year, with all three losses to Novak Djokovic. They could meet in the final next Sunday.

Six other seeded men lost: No. 10 Jurgen Melzer, No. 18 Marin Cilic, No. 20 Albert Montanes, No. 22 Marcos Baghdatis, No. 26 Juan Ignacio Chela, and No. 28 Ernests Gulbis. Melzer was beaten by friend and doubles partner Philipp Petzschner 3-6, 4-6.

No. 13-seeded Mikhail Youzhny drubbed Lu Yen-hsun of Chinese Taipei 6-1, 6-0 and No. 15 Jo-Wilfried Tsonga beat Teymuraz Gabashvili 6-3, 6-7 (3), 6-3.

In women's play, No. 16 Maria Sharapova advanced to a fourth-round matchup against No. 4 Samantha Stosur by beating Sabine Lisicki 6-2, 6-0. No. 11 Svetlana Kuznetsova, the 2006 champion, however, lost to China's Peng Shuai 3-6, 1-6.