ROME (AP) -- Top-ranked Serena Williams has withdrawn from the Italian Open.

Tournament organizers announced Williams' decision without explanation shortly before she was scheduled to face fellow American Christina McHale, a qualifier, in the third round. Williams was scheduled to meet with reporters later.

In her opener Tuesday, Williams cruised past 39th-ranked Anastasia Pavlyuchenkova 6-1, 6-3 in just over an hour.

The Italian Open is the last major warmup for the French Open, which starts in 10 days. Williams is the defending champion at the Foro Italico.

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