World No. 1 Serena Williams needed all three sets to win her second-round match, while her former top-ranked sister Venus exited the draw Wednesday at the $2.37 million Western & Southern Open, a hardcourt U.S. Open tune-up.

The biggest shock, though, came when Frenchwoman Marion Bartoli, the No. 8 seed and last month's Wimbledon champ, announced her retirement following a loss to Romanian Simona Halep, 3-6, 6-4, 6-1.

"That was actually the last match of my career. Sorry," Bartoli said at the post match press conference. "It's time for me to retire and call it a career. I feel it's time for me to walk away actually."

The 28-year-old Bartoli leaves the tour ranked seventh in the world and with eight career WTA singles titles. The highlight came at Wimbledon with her title victory over Sabine Lisicki.

"My body just can't do it anymore. I've already been through a lot of injuries since the beginning of the year," Bartoli said. "I've been on the tour for so long, and I really pushed through and left it all during that Wimbledon. I really felt I gave all the energy I have left in my body. I made my dream a reality and it will stay with me forever, but now my body just can't cope with everything. I have pain everywhere after 45 minutes or an hour of play. I've been doing this for so long, and body-wise I just can't do it anymore."

Following an opening-round bye, the reigning U.S. and French Open champ Serena lost the opening set against qualifier and rising Canadian Eugenie Bouchard before charging back for a 4-6, 6-2, 6-2 decision at the Lindner Family Tennis Center. The American needed 1 hour, 47 minutes to advance, which she did with the help of seven aces and six breaks of serve.

Serena, fresh off her title in Toronto last week, will encounter German Mona Barthel in the third round on Thursday.

An unseeded, world No. 37 Venus, meanwhile, succumbed to Russian Elena Vesnina 6-2, 5-7, 6-2. The 33-year-old Venus has now lost five of her last six matches on tour.

Meanwhile, fourth seed Agnieszka Radwanska of Poland defeated American Varvara Lepchenko, 6-4, 6-0; No. 5 seed and defending champion Li Na of China rallied past American Lauren Davis, 4-6, 6-1, 6-1; sixth-seeded former French Open runner-up Sara Errani of Italy snuck past Slovenian qualifier Polona Hercog 6-4, 5-7, 6-4; and seventh-seeded former Wimbledon champion Petra Kvitova fought off qualifier Marina Erakovic of New Zealand 6-4, 6-7 (7-9), 6-3.

Ninth-seeded German and 2012 Cincy runner-up Angelique Kerber beat Russian Alisa Kleybanova 7-6 (7-3), 6-2, while 10th-seeded former world No. 1 Caroline Wozniacki bested Romanian lucky loser Monica Niculescu 6-4, 6-3, and 11th- seeded former U.S. Open champion Samantha Stosur of Australia handled American Jamie Hampton 6-3, 7-6 (7-3). Stosur was the titlist in Carlsbad just two weeks ago.

Also on Day 3, 12th-seeded Italian Roberta Vinci held off German qualifier Andrea Petkovic 6-4, 6-7 (3-7), 6-3, 14th-seeded former No. 1 Jelena Jankovic overcame Russian Ekaterina Makarova, 2-6, 6-3, 6-3, and the aforementioned Barthel vanquished 16th-seeded Russian Maria Kirilenko 6-4, 6-4. The Serbian Jankovic titled here in 2009 and was the runner-up in 2011.

Another result saw Slovak Magdalena Rybarikova defeat France's Alize Cornet 3-6, 7-5, 7-5. Rybarikova is rewarded with a third-round match against second- seeded former top-ranked star Victoria Azarenka.

This week's winner will earn $426,000. The tournament is part of the U.S. Open Series, or the North American hardcourt events that lead up to the U.S. Open, which will commence August 26.