Trailing 3-0 in the first set, Williams had the tape on her right thigh removed. She won only nine points in the set, five on her serve.

"I was hitting really well yesterday and moving well," Williams said. "But before warmup I saw the trainer and said, 'Something's not right."'

The sixth-seeded American was treated again between sets. Winning only one more point, she was broken twice before retiring.

"I hate to quit. I'm not a quitter," Williams said. "I don't like people to think, 'She gave up.' Maybe I worry too much about what other people say."

Schnyder said she was just waiting to see what Williams would do.

"I was checking out the situation a bit and after the first set I kind of suspected she might retire," Schnyder said. "But then I got kind of nervous because in the second set she really started trying."

Williams, who has qualified for the season-ending WTA Championship, had asked to play today despite coming off a three-set loss to Elena Dementieva at the Kremlin Cup in Moscow on Sunday. She reached the quarterfinals in Stuttgart, Germany, the week before.

"Normally she needs a rest after two weeks of tournaments," Schnyder said. "But I like that she came here and tried."