SEA ISLAND, Ga. -- A thigh injury forced Anna Kournikova to withdraw from the Cloister Cup before her semifinal match.

Kournikova quit the tournament Saturday after a practice earlier in the day. The withdrawal advanced fellow Russian Maria Sharapova to the final, where she beat Australian Christina Wheeler 6-4, 6-3 on Sunday.

Kournikova was first injured April 9 at the Family Circle Cup in Charleston, S.C.

She struggled through her quarterfinal match against Sunitha Rao on Friday, which she won 6-3, 6-3. Kournikova's tightly wrapped thigh gave her problems throughout the match, and she was limping by the end.

The Cloister Cup was Kournikova's first event since she was first injured.