Andrea Petkovic improves to 10-0 at Family Circle with win over American Madison Brengle

Andrea Petkovic of Germany, hits against Madison Brengle during the third round of the Family Circle Cup tennis tournament in Charleston, S.C., Thursday, April 9, 2015. Petkovic beat Brengle 6-4 6-4. (AP Photo/Stephen B. Morton) (The Associated Press)

Andrea Petkovic of Germany, reacts to a shot against Madison Brengle during the third round of the Family Circle Cup tennis tournament in Charleston, S.C., Thursday, April 9, 2015. Petkovic beat Brengle 6-4 6-4. (AP Photo/Stephen B. Morton) (The Associated Press)

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.