MADRID, Spain - The first round wrapped up and the second round began at the Mutua Madrileña Madrid Open on Monday, and one of its biggest draws - Serena Williams - was among the casualties, succumbing to injury.

Williams, the No.2 seed, lost the first set to Francesca Schiavone, 6-4, then was forced to retire from the match due to a right knee injury. It was the world No.2's fourth straight loss: she fell to Victoria Azarenka in the final of Miami then suffered back-to-back opening round exits at Marbella and Rome, to Klara Zakopalova and Patty Schnyder.

"I wanted to do well here, but I was really hindered and I didn't want it to get worse. I didn't want to risk my chances to play Roland Garros," a dejected Williams said. "It's something that has bothered me in the previous weeks. It's always hard to deal with things like this. I came here to compete and do my best. I planned on doing well. But you just live to fight another day, I guess."

Rounding out the first round winners were No.9 seed Caroline Wozniacki, Amélie Mauresmo, Peng Shuai, Daniela Hantuchova and qualifiers Roberta Vinci and Varvara Lepchenko. Wozniacki won when Shahar Peer retired with a foot injury.

The first batch of second round matches also took the court on Monday, with No.8 seed Nadia Petrova surviving a marathon against qualifier Anna-Lena Groenefeld, 46 76(3) 76(5); Schnyder beating Aleksandra Wozniak, 62 64; Anna Chakvetadze rallying from 4-1 down in the third to edge Samantha Stosur, 16 62 76(4); and qualifier Elena Vesnina outdoing Virginie Razzano, 75 63. Later in the day, No.3 seed Elena Dementieva faced wildcard Lourdes Domínguez Lino and eased past the tenacious Spaniard in straight sets, 63 62.

There was plenty of doubles action on Day 3 as well, with Nuria Llagsotera Vives and María José María José Martínez Sánchez - the new Race to the Sony Ericsson Championships doubles points leaders and the No.5 seeds here - among the winners, beating last week's Estoril champions Raquel Kops-Jones and Abigail Spears in their first round match, 76(5) 62. Hantuchova and Ai Sugiyama, runners-up at Rome last week and the No.7 seeds here, also advanced.