NEW YORK — Venus Williams landed awkwardly on her recently injured leg after hitting a swinging volley and grimaced. It was about the only glitch during her return to tennis.

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.

“It was doing pretty good, till I landed on that leg on the swing volley. … I was pretty happy to get through after not playing in forever,” said Williams, whose younger sister Serena isn’t playing in the U.S. Open after surgery for deep cuts on her right foot.

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

Vinci knew, of course, about Williams’ recent time off, and said afterward with a sigh: “I hoped she would play worse.”

Two of the American’s seven Grand Slam titles came at Flushing Meadows, in 2000 and 2001, and other past U.S. Open champions Kim Clijsters and Andy Roddick also won on Day 1. Roger Federer took a 6-1, 6-4, 6-2 win over Brian Dubal in a night match.

But 32nd-seeded Lleyton Hewitt, who won the tournament in 2001, hit 12 double-faults and was upset by 109th-ranked Paul-Henri Mathieu of France 6-3, 6-4, 5-7, 4-6, 6-1.

“I wasn’t expecting a whole heap coming into this tournament, based on my preparation,” said Hewitt, who had played only four matches, losing three, since Wimbledon.

Monday’s loss is Hewitt’s only first-round exit in 11 trips to the U.S. Open. Williams, meanwhile, improved to 12-0 in opening matches in New York, and 48-3 in openers at all major tournaments.

She hadn’t competed since being upset in the Wimbledon quarterfinals June 29 by then-No. 82 Tsvetana Pironkova of Bulgaria. Pironkova won Monday, too, and Williams could face her in the third round.

Roddick turned 28 on Monday, 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.”

Well, that’s true. He also, however, is seven years older than he was when he won his lone Grand Slam title at the 2003 U.S. Open. There’s a reminder of that accomplishment every time Roddick returns to Flushing Meadows: His spot in the locker room bears a special plate with his name and the year he was the champion, a bit of recognition he referred to as “the little deal on your locker that says you’re special.”

Clijsters is “special,” too. The Belgian won the U.S. Open each of the last two times she entered, in 2005 and 2009, and she stretched her winning streak in New York to 15 matches Monday despite a brief blip.

The No. 2-seeded Clijsters began her title defense with a 6-0, 7-5 victory over 104th-ranked Greta Arn of Hungary. It was an afternoon of mostly straightforward results, although two-time French Open runner-up Robin Soderling was stretched to five sets before edging 214th-ranked qualifier Andreas Haider-Maurer, who pounded 34 aces.

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, while No. 27 Fernando Gonzalez quit in the third set of his match against Ivan Dodig because of a knee injury.

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, two-time major finalist Elena Dementieva, No. 10 Victoria Azarenka, No. 13 Marion Bartoli, No. 16 Shahar Peer, and No. 24 Daniela Hantuchova, who beat former No. 1 and current No. 50 Dinara Safina 6-3, 6-4. Another past No. 1 now sitting way down in the rankings, No. 40 Ana Ivanovic, reached the second round by eliminating Ekaterina Makarova 6-3, 6-2.

Williams got off to a good start against Vinci, leading 3-0 and 4-1. But the Italian reeled off three consecutive games and 10 of 12 points to pull completely even at 4-all, 30-all.

That’s when Williams took over, delivering an overhead smash on the next point, followed by her fifth ace, at 115 mph, to hold for a 5-4 lead. Williams then broke Vinci at love, giving her six points in a row to close the first set.