Wozniacki advances, Stosur falls in rain-altered Family Circle Cup

Former champion Caroline Wozniacki secured a quarterfinal berth without lifting her racquet Thursday at the Family Circle Cup tennis event.

The second-seeded former world No. 1 star was scheduled to meet Andrea Petkovic on Day 4, but the oft-injured former top-10 German pulled out of the draw due to a calf injury.

Wozniacki, a runner-up at Indian Wells a few weeks ago, titled on the green clay here at Daniel Island Tennis Center in 2011 and was the runner-up back in 2009.

An injury also led to the ousting of third-seeded Samantha Stosur, with the Australian veteran retiring in the second set of her match with Canadian Eugenie Bouchard due to a calf strain.

Stosur, the Family Circle titlist in 2010, was down 6-1, 2-0 to Bouchard when dropping out.

Inclement weather forced four of Thursday's scheduled third-round matches to be postponed until Friday, including ones involving American sister stars Serena and Venus Williams.

The top-seeded Serena was slated to face countrymate Mallory Burdette, with fifth-seeded Venus to take on No. 12 seed Varvara Lepchenko.

Sixth-seeded Lucie Safarova, who fell to Serena Williams in last year's final here, also had her match with No. 11 seed Sorana Cirstea moved back, as did a clash between Americans Bethanie Mattek-Sands and Madison Keys.

Wozniacki will next meet Stefanie Voegele in the quarters after the Swiss native outlasted 10th-seeded German Julia Goerges by a 3-6, 6-1, 6-3 count.

Bouchard's victory sets up a showdown with 2007 Charleston champ Jelena Jankovic after the ninth-seeded Serb disposed of American qualifier Jessica Pegula 6-0, 6-4.

The winner of this $795,000 tournament will earn $125,000.