Svetlana Kuznetsova became the first player to reach the last four of the WTA Finals following victory over Karolina Pliskova in Singapore.
Kuznetsova, 31, beat Czech Pliskova 3-6 6-2 7-6 (8-6) but her semi-final spot was sealed by Agnieszka Radwanska's 7-6 (7-1) 6-3 win over Garbine Muguruza.
Defeat eliminated Spain's Muguruza at the group stage.
The winner of Polish defending champion Radwanska's final White Group match with Pliskova will also go through.
Both Kuznetsova and Pliskova served for the match in the third set, before Kuznetsova converted her fourth match point,
"I felt the support of the crowd and I couldn't let anyone down.