Agnieszka Radwanska will play world number one Angelique Kerber in the WTA Finals last four after beating Karolina Pliskova 7-5 6-3.
The Polish defending champion overcame Finals debutant Pliskova in 78 minutes.
French Open champion Garbine Muguruza avoided a whitewash at the event as she beat Svetlana Kuznetsova 3-6 6-0 6-1 in their dead rubber.
Russian Kuznetsova was already through as group winner with Muguruza out after defeats in her first two matches.
Kuznetsova, who only qualified for the tournament with victory at the Kremlin Cup in Moscow on Saturday, will meet Slovak world number eight Dominika Cibulkova in Saturday's other semi-final.