Defending champion Andrea Petkovic kept up her perfect run at the Family Circle, improving to 10-0 and advancing to the quarterfinals with a 6-4, 6-4 win over American Madison Brengle on Thursday.

The third-seeded Petkovic is the highest-ranked player left after No. 1 seed Eugenie Bouchard lost Wednesday night only hours after No. 2 seed Ekaterina Makarova withdrew with a stomach illness.

Petkovic rallied from 2-1 deficits in both sets to move on. She'll face either No. 6 seed Jelena Jankovic or qualifier Danka Kovinic, who will play Thursday night.

American Lauren Davis, who ousted Bouchard, advanced into the quarterfinals after Mona Barthel retired while trailing 6-4, 3-0.

Eight-seeded Carolina Garcia lost to qualifier Lucie Hradecka in three sets. Fifth-seeded Angelique Kerber also advanced with a 6-3, 6-0 win over Lara Arruabarrena.