NEW YORK - Once you reach a certain age, birthdays tend to make you reflect on your own mortality. They also, in the case of a professional athlete such as Andy Roddick, tend to prompt questions about the state of your career.

Roddick turned 28 on Monday, Day 1 of this year's U.S. Open, and after beating Stephane Robert of France 6-3, 6-2, 6-2, the ninth-seeded American was asked what significance he attributes to his age.

In typical Roddick fashion, he injected his reply with some humor.

"Obviously, I know I'm probably closer to the finish than I am to the start," he said. "But ... it's a number. I'm barely older than I was yesterday."

The No. 2-seeded Clijsters began her title defense with a 6-0, 7-5 victory over 104th-ranked Greta Arn of Hungary.

Playing for the first time in two months after spraining her left kneecap, seven-time Grand Slam champion Williams beat Roberta Vinci of Italy 6-4, 6-1 Monday night to reach the U.S. Open's second round.

She hit 10 aces, reaching 126 mph, and became only the fifth woman with 200 career victories at major tournaments

Roger Federer hit a back-to-the-net, between-the-legs winner and smacked 18 aces while eliminating Argentina's Brian Dabul 6-1, 6-4, 6-2 at night.

Other winners included No. 6 Nikolay Davydenko, No. 11 Marin Cilic, No. 13 Jurgen Melzer, No. 17 Gael Monfils and No. 22 Juan Carlos Ferrero.

Women moving into the second round included surprise 2009 U.S. Open quarterfinalist Melanie Oudin, French Open champion Francesca Schiavone, French Open runner-up Sam Stosur, Elena Dementieva, and No. 10 Victoria Azarenka.