Andrea Petkovic withdrew from the Family Circle Cup before her scheduled Thursday morning match against No. 2 seed Caroline Wozniacki, allowing the 2011 Family Circle Cup champion to advance to Friday’s quarterfinals in a walkover.

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Petkovic, from Germany, is unseeded but finished the 2011 WTA season ranked No. 10. She tweeted that she is suffering from a right calf injury.

To fill the 11 a.m. Petkovic/Wozniacki spot, the Bethanie Mattek-Sands/Madison Keys match has been moved from the Althea Gibson Court to the Billie Jean King Court for an 11 a.m. start.

Rain is in the forecast all day Thursday but the Family Circle Cup schedule remained intact.

Follow Gene Sapakoff on Twitter @sapakoff