Ninth seed Marion Bartoli was the biggest early casualty in the Rogers Cup in Toronto as she fell to a 6-3 6-3 first-round defeat to Kazakh qualifier Galina Voskoboeva.
The world number 135 needed an hour and 15 minutes to pull off one of the best wins of her career against France's Wimbledon semi-finalist. Voskoboeva hit three aces and saved two out of three break points.
Three more seeds also crashed out.
Russian 12th seed Svetlana Kuznetsova was beaten 4-6 6-4 6-3 by Romanian Simona Halep, and Spain's Maria Jose Sanchez Martinez knocked out 14th-seeded Russian Anastasia Pavlyuchenkova 3-6 6-4 6-1.
Germany's Julia Goerges posted a surprisingly easy 6-1 6-3 win against Serbian 15th seed Jelena Jankovic.
Australian 10th seed Samantha Stosur moved through but not without a fright, losing the first set of her match to Japan's Ayumi Morita before rallying to pull off a 4-6 6-2 6-3 win in just under two hours.
Nadia Petrova eased past Jarmila Gajdosova 6-1 6-2 while other early winners included qualifier Greta Arn, who beat Klara Zakopalova, Lucie Safarova and Jie Zheng.
In later action, Russian Ekaterina Makarova scrapped out a 7-6 (8/6) victory over Canadian Rebecca Marino.
The world number 135 needed an hour and 15 minutes to pull off one of the best wins of her career against France's Wimbledon semi-finalist. Voskoboeva hit three aces and saved two out of three break points.
Three more seeds also crashed out.
Russian 12th seed Svetlana Kuznetsova was beaten 4-6 6-4 6-3 by Romanian Simona Halep, and Spain's Maria Jose Sanchez Martinez knocked out 14th-seeded Russian Anastasia Pavlyuchenkova 3-6 6-4 6-1.
Germany's Julia Goerges posted a surprisingly easy 6-1 6-3 win against Serbian 15th seed Jelena Jankovic.
Australian 10th seed Samantha Stosur moved through but not without a fright, losing the first set of her match to Japan's Ayumi Morita before rallying to pull off a 4-6 6-2 6-3 win in just under two hours.
Nadia Petrova eased past Jarmila Gajdosova 6-1 6-2 while other early winners included qualifier Greta Arn, who beat Klara Zakopalova, Lucie Safarova and Jie Zheng.
In later action, Russian Ekaterina Makarova scrapped out a 7-6 (8/6) victory over Canadian Rebecca Marino.