Serena Williams is back. In fact, one can hardly miss her.

Struggling of late with a knee that was surgically repaired last year, Williams returned to the U.S. Open last night after missing the tournament last year. She walked into Arthur Ashe Stadium just before 8 p.m. in her latest fashion statement of choice – a denim skirt, black studded tank top cut off above the stomach, and black sneakers – and made quick work of her overmatched opponent, Sandra Kleinova of the Czech Republic, 6-1, 6-3.

Cheers rang through the crowd when Kleinova, 27, won a game after dropping the first three. The Czech scored a big upset over Russia’s Elena Dementieva at Wimbledon this year, but last night she didn’t look like much more than a practice partner for Williams. The American was barely tested, and seemed to move with ease when she had to chase down a short shot (which she converted into a deft drop-shot winner) or charge a floating return (which she smacked with a swinging forehand volley).

Williams, who defeated her sister Venus to win the 2002 U.S. Open, warmed up before the match in her new line of breathable boots, but said they were too warm for August tennis in New York. She dubbed her new line of clothing, which she designed herself, the “Rebel Without a Cause Line.” And yes, she said she felt good about her tennis, too.

“I think I performed at a pretty decent level today,” she said. Asked if she would rather have had to sweat more for her victory, she said, “I think everyone out here would prefer to win their matches really easy.”

Before Serena cruised to a nighttime win, her compatriot, eighth seed Jennifer Capriati, struggled mightily on a muggy day before advancing against another Czech, unseeded Denisa Chladkova, 2-6, 6-1, 6-2.

The early part of the match was a contest of contrasts. Capriati, the prototypical modern tennis player who relies on short strokes and quick bursts of power, was unable to solve the less flashy Chladkova, who takes a long, looping backswing on her forehand and nearly touches her knee to the ground when striking her two-fisted backhand.

For about 30 minutes, Capriati took it on the chin. Chladkova, a 25-year-old who lost in the first round at the Pilot Pen in New Haven last week, ran the American ragged, working the ball side to side and chasing down everything Capriati threw at her. She showed patience, and when she found an opening, she snapped off winners that had as little spin as any ever hit by the master of the flat ball himself, Jimmy Connors.

With Chladkova leading 6-2, 1-0, a fan shouted to Capriati, “You’ve got to wake up!” A game later, she responded. First she protested a missed line call and earned herself a code violation for foul language. Moments later, she returned a 66 mph second serve for a winner and a service break.

Capriati ran away with it from there, losing just two more games. Afterward she said she had a difficult time adjusting to the wind and Chladkova’s low-lying bullets.

“She came out playing really great tennis, cleaning the lines,” Capriati said. “It was just a few important points that I was able to win. I think it changed the momentum a little bit.”

Capriati may have a long way to go before she returns to the form that brought her to the semifinals at last year’s Open, but she says she was at least glad that Chladkova gave her an opportunity to work out some kinks. “I definitely practiced everything out there, you know, between the mental and the physical.”

In the day’s first match on Arthur Ashe, second seed Amelie Mauresmo of France walked off with any easy victory over Marissa Irvin, 6-4, 6-2. The talented Mauresmo has had another strong year, but for all her promise, she has yet to win a big tournament. She recently added the Olympics to her list of almost-victories, losing the gold medal match to Justin Henin-Hardenne. Still, Mauresmo said she does not feel like her time for a Grand Slam is now or never.

“I don’t feel more pressure here than Wimbledon or the Australian Open,” she said. “French Open is a little different for me.”

In other women’s matches, sixth seed Dementieva escaped a firstround upset when she defeated countrywoman Dinara Safina, Marat Safin’s sister, 2-6, 6-1, 6-2. American Meghan Shaughnessy was not so lucky: She was upset by Marion Bartoli of France, 6-4, 6-4. In another upset, Croatia’s Jelena Kostanic defeated 18th seed Karolina Sprem, also of Croatia, 6-3, 2-6, 6-4. It was their first meeting as professionals.