Defending champion Roger Federer [Images] stuttered into the fourth round of the U.S. Open on Sunday with a 6-3, 7-6, 6-2 victory over Belgian Olivier Rochus, the 27th seed.

The top seed struggled for his rhythm but clinched victory in just less than two hours to move into the last 16 without dropping a set.

He will now play German Nicolas Kiefer, the only man to capture a set from him during his run to the Wimbledon [Images] title this year.

"We played tough matches at Cincinnati and Wimbledon," Federer said of Kiefer.

Federer lost the opening set in Cincinnati before winning the final two, and needed four sets in the Round of 32 at Wimbledon to dispatch Kiefer.

"He's improved a lot in the last few months and I expect it to be a tough match," said Federer.

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Federer took advantage of just one service break to win the opening set. In the second set, he recovered from an early break and then came back from a 4-1 deficit in the tiebreak to win it, 8-6.

That relaxed Federer and he broke Rochus twice in the final set to seal the victory.

Federer and the 5-foot-5 (1.65 meters), 130-pound (59 kilograms) Rochus would often play together as juniors, and teamed up to win the 1998 junior doubles title at Wimbledon.

"I already had the feeling when we were 14 that he was already playing at an incredible level," Federer said.

"But I grew a bit and got stronger, and then things changed. But it is great to see him on the tour and he does an incredible job at his height to play with the best and sometimes beat them."

The victory over Rochus raised Federer's winning streak on hard courts to 31 matches, dating back to his defeat by eventual champion Marat Safin [Images] in the semi-final of the Australian Open [Images] in January.

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