A gutsy Elina Svitolina willed herself to the semi-finals after overcoming Caroline Wozniacki in a gruelling three-set match, knocking the defending champion out of the WTA Finals here.

The unbeaten Ukrainian outlasted Wozniacki 5-7, 7-5, 6-3 in two hours and 35 minutes to finish top of White Group. Karolina Pliskova also qualified after the Czech defeated compatriot Petra Kvitova 6-3, 6-4.