Maria Sharapova's perfect start to the year came to a shuddering halt when she was beaten 6-3, 5-7, 6-2 by fellow-Russian Svetlana Kuznetsova in the Pacific Life Open semi-finals on Friday.
Australian Open champion Sharapova, who had won her first 18 matches of the season, was outplayed by her compatriot in a fluctuating match lasting two hours, 19 minutes.
Kuznetsova made the most of an error-strewn display by her opponent to sweep through the first set in 46 minutes, Sharapova double-faulting five times and making 20 unforced errors.
After service breaks were traded in the second and seventh games of the second set, Sharapova levelled the match when Kuznetsova double-faulted at 30-40 to be broken in the 12th game.
However, the 2004 US Open champion piled on the pressure in the final set, breaking Sharapova in the first game and again in the fifth with a superb forehand winner down the line.
The 22-year-old Kuznetsova calmly booked her place in the final by serving out to love in the eighth game, a protracted last rally ending when Sharapova's speculative lop landed long.
It was Kuznetsova's fourth victory against Sharapova in eight career meetings.
Top-seeded Ana Ivanovic was scheduled to play fellow Serb Jelena Jankovic, the third seed, in an evening match for the other spot in Sunday's final.