KEY BISCAYNE, Fla. -- Fifth-seeded Angelique Kerber eked out a victory in her opening match Thursday at the Sony Open, beating Peng Shuai 6-3, 1-6, 7-6 (5).

Kerber, a two-time Grand Slam semifinalist, matched her best showing at Key Biscayne by reaching the third round.

No. 12 Ana Ivanovic beat American Lauren Davis 6-1, 6-1, and No. 28 Svetlana Kuznetsova, the 2006 champion, lost to qualifier Donna Vekic 7-6 (5), 7-5.

On the men's side, Americans Jack Sock and Ryan Harrison won first-round matches. Sock, a qualifier, beat wild card Guido Pella 6-3, 6-4. Harrison, a wild card, defeated Federico Delbonis 6-2, 6-4.

Six-time champion Serena Williams and Maria Sharapova were scheduled to play their opening matches later Thursday. Seeded men begin play on Friday.