LOS ANGELES - Mary Pierce won her 500th career match, defeating Elena Dementieva of Russia 6-2, 6-3 in the WTA Championships on Wednesday night.

Pierce improved to 2-0 in round-robin play, including her three-set upset of Kim Clijsters on opening night.

Top-ranked Lindsay Davenport played Patty Schnyder of Switzerland and Clijsters faced Amelie Mauresmo of France in later matches.

The oldest player in the eight-woman field at 30, Pierce put herself in good position to reach the semifinals, which are single elimination.

Pierce is the third active player after Conchita Martinez and Lindsay Davenport to reach 500 wins.

Playing in the season-ending championships for the first time since 1999, Pierce used big serves and sharp volleys against Dementieva, whom she beat in the U.S. Open semifinals.

Pierce collected all three service breaks in the first set, winning when Dementieva double-faulted. The Frenchwoman broke for a 2-0 lead in the second set, then rallied from love-40 on her serve to go up 3-0.

She faltered briefly leading 4-2, losing serve on a double fault. But Dementieva missed a forehand to fall behind 5-3 and then netted a backhand volley on match point.

Dementieva fell to 1-8 in the championships since 2000, when she was a semifinalist in her debut.

The players are assigned to Green and Black groups and play each other once. The two players with the best record from each group advance to the semifinals.

Pierce leads the Black group with a 2-0 record.