ZURICH, Switzerland (AP) -- Serena Williams retired with a sore right thigh while trailing Patty Schnyder of Switzerland 6-0, 3-0 in the first round of the Zurich Open on Tuesday.
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 Tuesday 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."
Williams said she has no other tournaments planned before next month's WTA event in Madrid, Spain.
Amelie Mauresmo struggled to beat Eleni Daniilidou of Greece 6-4, 4-6, 6-3, and Wimbledon finalist Marion Bartoli advanced by defeating Peng Shuai of China 6-7 (4), 6-0, 6-1.
Mauresmo capitalized on her opponent's ankle troubles in the third set, jumping out to a 5-2 lead and winning on her next serve.
"It would have been surprising for me to play my best tennis in the first round here and win in two quick sets," Mauresmo said. "The main thing was to win. That's what I've been focusing on recently."
The two traded breaks midway through the first set, but last year's Wimbledon and Australian Open champion held on to take the lead.
Daniilidou had her ankles taped before the start of the second set, and then broke Mauresmo in the opening game. The Frenchwoman recovered her serve, but soon fell apart and trailed 4-1.
"I would have preferred to finish in the second set but I knew a third set would be difficult for her even if she was moving really well," Mauresmo said.
Mauresmo, a former top-ranked player, has struggled since having an appendectomy in March.
"My surgery really killed me for the rest of the season. I definitely haven't been playing my best tennis for a few months now," Mauresmo said.