Serena withdraws at Madrid Open

MADRID, May 11 (UPI) -- Former world No. 1 Serena Williams retired after one set Monday in her opening-round match at the $4.5 million Madrid Open.

Williams, seeded No. 2, lost the first set 6-4 against Italian Francesca Schiavone before bowing out with a right knee injury.

"I was just really hindered," said Williams, current Australian Open and U.S. Open champion. "My movement was hindered as a result of an injury I've been struggling with for some time. I'm trying to compete and do my best, and it didn't work out."

Also Monday, Olympic gold medalist and third-seeded Elena Dementieva defeated Spaniard Lourdes Dominguez Lino 6-3, 6-2.

In other matches involving seeds, Russian Nadia Petrova beat German Anna-Lena Groenefeld 4-6, 7-6 (7-3), 7-6 (7-5) and Dane Caroline Wozniacki was leading Shahar Peer 5-4 in the first set when the Israeli dropped out.