New York ? Wearing what she described as her “micro-mini” outfit, third-seeded Serena Williams advanced to the third round of the U.S. Open on Wednesday with a 6-4, 6-3 victory over Lindsay Lee-Waters.

It was not easy, the former Open champion said.

“It was a great test,” Williams said. “She hits the living daylights out of the ball. She was killing everything.”

Williams said she felt at ease in the first two rounds of the open, relaxed and calm with nothing to lose.

And as for her outfit — a black, studded tank top that revealed her midriff and matching tight shorts — she simply smiled.

“I have another surprise for the next match,” she said.

Second-seeded Amelie Mauresmo almost was surprised, dropping the first set to Julia Vakulenko. But Mauresmo recovered to win, 3-6, 6-2, 6-2, to reach the third round.

Mauresmo overcame 34 unforced errors and 10 double faults and finished the match with her fourth ace.

“I started very slow in the first set,” said Mauresmo, who won the silver medal at Athens. “I’m looking forward to improve my game because I am not satisfied now.”

Angela Haynes, ranked 185th, tasted her first bit of Grand Slam success, defeating 22nd-seeded Magdalena Maleeva, 6-2, 6-3, to reach the third round.

Gustavo Kuerten, the former French Open champion who was seeded No. 20, was a first-round loser, beaten by Kristian Pless, 6-4, 3-6, 6-1, 7-6 (4). Kuerten was done in by 40 unforced errors.

Earlier, fourth-seeded Lleyton Hewitt began his Open with an efficient 6-1, 7-5, 6-4 victory over Wayne Ferreira in the 57th and final Grand Slam tournament for the veteran South African.