Bartoli won only 22 percent of the points on her second serve. Peng broke her three times, including the opening game of the second set.
Second-seeded Alona Bondarenko also won, beating Edina Gallovits of Romania 6-4, 6-4. Bondarenko, who broke her opponent's serve five times, next plays Timea Bacsinszky, who beat Yan Zi of China 6-2, 5-7, 6-4.
Fourth-seeded Flavia Pennetta of Italy and Katarina Srebotnik of Slovenia also advanced to the last eight. Pennetta defeated Stephanie Cohen-Aloro of France 6-3, 4-6, 6-3, while Srebotnik advanced by beating Tatiana Perebiynis of Ukraine 7-6 (4), 6-0.
Also, defending champion Anabel Medina Garrigues of Spain beat Ana Vrljic 6-1, 6-1, Ai Sugiyama of Japan saved all five break points before beating Petra Kvitova 6-4, 6-3, and 18-year-old Chan Yung-jan of Taiwan rallied to beat Casey Dellacqua of Australia 2-6, 6-1, 6-1.
The clay-court tournament is billed as a warmup to the French Open, which starts Sunday.
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