Matches for top-ranked Serena Williams and her sister, Venus, at the Family Circle Cup were postponed Thursday after a rain delay of nearly 7 1/2 hours.

Play began around 6:30 p.m. with ninth-seeded Jelena Jankovic facing American qualifier Jessica Pegula on the Althea Gibson court by the clubhouse. Crews were drying off the main Billie Jean King Court for a pair of matches featuring 10th-seeded Jula Goerges and third-seeded Samantha Stosur.

Earlier, Andrea Petkovic withrew from the tournament because of a right calf injury, moving second-seeded Caroline Wozniacki into the quarterfinals.

Petkovic apologized for pulling out, but felt she might do more damage to her leg if she competed.

Wozniacki, the 2011 Family Circle champion, will play either Goerges or Stefanie Voegele in the quarterfinals.