Petrova had been enjoying the form of her life during the claycourt season earlier this year -- winning three consecutive tournaments -- but a groin injury picked up in the run-up to the French Open [ Images ] appears to have completely thrown her off course.

The left leg strain put paid to her Roland Garros [ Images ] campaign, where she lost in the opening round, and after opting out of the tour for two months to recuperate, she has failed to win a match in three attempts since making her comeback.

Chakvetadze, who also beat Petrova in San Diego earlier in the month, will next play Nathalie Dechy [ Images ] of France [ Images ], who knocked out 15th-seeded Russian Maria Kirilenko 6-4 6-4.

Fellow Russian Anastasia Myskina [ Images ] continued her unpredictable run of form by exiting at the hands of Israel's Shahar Peer.

The sixth seed went down 7-6 5-7 6-4 for her second defeat at the first hurdle in three tournaments after reaching the final in Stockholm last week.

Fourth seed Svetlana Kuznetsova [ Images ] had little difficulty moving on, defeating Polish qualifier Marta Domachowska 6-1 6-3.

Other seeded players also fell to the wayside on Wednesday, with American qualifier Shenay Perry outslugging 10th seed Anna-Lena Groenefeld of Germany [ Images ] 7-6 6-2.

Serbia's Jelena Jankovic [ Images ] defeated number eight Francesca Schiavone of Italy [ Images ], 6-1 6-4, and Japan's [ Images ] Ai Sugiyama [ Images ] upset 17th seed Anabel Medina Garrigues of Spain 6-4 6-2.

Italy's Flavia Pennetta [ Images ], the 12th seed, had to retire in the second set trailing 7-5 2-1 against France's Marion Bartoli [ Images ].

Russia's [ Images ] Dinara Safina [ Images ] and Daniela Hantuchova [ Images ] of Slovakia were among the seeded winners.

Top seed Kim Clijsters [ Images ], the U.S. Open champion, begins her title defence against local wildcard Stephanie Dubois in the featured evening match.