Pliskova shows grit to advance
Karolina Pliskova won a see-saw match against Simona Halep to claim the last semi-final spot at the WTA Finals in Shenzhen.
The World No.2 ran away with the first set but dropped the second and trailed 2-0 in the decider.
But Wimbledon champion Halep, the fifth seed, then went completely off the boil as Pliskova came back to win 6-0 2-6 6-4.
Czech Pliskova will face Ashleigh Barty of Australia in the last-four.
Earlier, defending champion Elina Svitolina ensured she remained unbeaten in the group stage after dispatching alternate Sofia Kenin of the United States.
The eighth seed had already been assured of a place in the semi-finals but she still battled hard for a 7-5 7-6 (10) win in two hours and 10 minutes.
Svitolina said: "Each time I step on the court I have to win. My parents raised me this way - I have to fight for everything, I have to give 100 per cent each time I play."
Svitolina will face seventh seed Belinda Bencic for a place in the final.