Serena Williams of the U.S. receives medical attention during her second-round match against Chan Yung-Jan of Taiwan during the Family Circle Cup tournament in Charleston, South Carolina, on Tuesday night. Williams was forced to withdraw from the event. - Reuters

CHARLESTON, South Carolina (AP):

SERENA WILLIAMS retired with a groin pull against Chan Yung-jan in her opening match at the Family Circle Cup on Tuesday.

Taiwan's Chan was up 5-3 when Williams withdrew, apologising to the crowd before she left stadium court.

Williams, the third seed, said she strained the muscle in Monday's practice and a trainer said it didn't seem like it would affect her play in future tournaments.

"But it could potentially get worse if I don't take care of it," added Williams, who played with her right thigh wrapped.

"I've been playing a lot on the clay and, like I said, I was just sliding a lot and I think I just slid too far," she said.

Earlier, Williams' sister Venus easily advanced, defeating Australia's Samantha Stosur 6-2, 6-2.

"I feel really good," said 29th-ranked Williams, playing in her fourth tournament after being sidelined for the last half of 2006 with a wrist injury. "I don't think of myself as an underdog. I just think of myself not being as highly ranked as I should be and that happens when you take time off."

Fell to wild card

Just hours before Serena Williams' withdrawal, top-seeded Nicole Vaidisova fell to wild card Michaella Krajicek of the Netherlands 4-6, 6-4, 6-3 - the first time in the tournament's 36-year history a top seed was bounced in her first match.

It was the only the second time in her career that 17-year-old Vaidisova, ranked No. 8 in the world, entered a tour event as a top seed. Again, as she was at Memphis last year, the Czech was eliminated in her first match.

"I didn't feel in any part of the match I played well," Vaidisova said. "I wasn't really hung up on the fact I was the No. 1 seed, but of course I'm disappointed."

Krajicek, sister of 1996 Wimbledon champion Richard Krajicek, avenged a three-set loss to Vaidisova last month at Key Biscayne.

"It's a great win," Krajicek said. "I was looking forward to a win like this, and especially when you beat the first seed."

Tatiana Golovin of France, who won her first tour title last week at Amelia Island, won 6-4, 6-1 over qualifier Dominika Cibulkova of Slovakia.

"I've never really played back-to-back tournaments after winning one," said Golovin, who added she has not had time to savour last week's win. She said she felt confident, but struggled because she was tired.

"You know what you can do and I'm playing well," said Golovin, who was treated for a blister on her toe during the match. "It's just a matter of how I'm going to be able to hold up physically."

Francesca Schiavone of Italy advanced 6-2, 2-0 when Virginia Ruano Pascual of Spain retired with a back injury.

Other first-round winners included Katarina Srebotnik of Slovenia, Sybille Bammer of Austria and Mara Santangelo of Italy.