Maria Sharapova opened her bid for a third Italian Open title with a win over 52nd-ranked Jarmila Gajdosova on Tuesday.
The third-seeded Sharapova was leading 6-2, 3-1 when her Australian opponent retired with an apparent injury.
Sharapova won back-to-back titles at the Foro Italico in 2011 and 2012. She is coming off a loss to Svetlana Kuznetsova in the Madrid Open semifinals.
Organizers did not immediately say why Gajdosova retired.
In men's action on the red clay, Guillermo Garcia-Lopez of Spain beat U.S. Open champion Marin Cilic 6-4, 6-3.
Later, top-ranked Novak Djokovic was to play Nicolas Almagro and Serena Williams was to face Anastasia Pavlyuchenkova.
The Italian Open is the last big warm-up tournament for the French Open, which starts in less than two weeks.
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