Katowice - Top-seeded Agnieszka Radwanska of Poland was overcome by Alize Cornet of France 0-6, 6-2, 6-4 in the Katowice Open semi-finals on Saturday.
Cornet will face first-time WTA finalist Camila Giorgi of Italy.
Radwanska didn't concede a set to Cornet in three previous matches, including at Indian Wells last month, and the hometown favorite won the first set quickly.
Cornet levelled, but Radwanska had a point for 4-0 in the third when she began to unravel.
Cornet won six of the last seven games for only her second career win over a top-three player.
She will play for her fourth career title against Giorgi, who beat third-seeded Carla Suarez Navarro of Spain 7-6 (2), 6-4.
Giorgi, who hadn't reached a WTA quarter-finals until this week, beat two top-20 players in the same tournament for the second time.
Alize Cornet (FRA x4) bt Agnieszka Radwanska (POL x1) 0-6, 6-2, 6-4
Camila Giorgi (ITA) bt Carla Suarez Navarro (ESP x3) 7-6 (7/2), 6-4