Simona Halep was branded an "absolute disgrace" by coach Darren Cahill as Karolina Pliskova came out on top in a crucial round-robin WTA Finals clash to reach the last four.

Pliskova and Halep went into the last Purple Group contest in Shenzhen on Friday knowing the winner would face top seed Ashleigh Barty at the semi-final stage and the loser's season was over.

Halep fought back following the humiliation of a first-set bagel, but Pliskova came from a break down in the final set to win 6-0 2-6 6-4.

The Wimbledon champion rallied following some words of wisdom from Cahill at the end of the first set, but the Australian said she had been "an absolute disgrace" over a critical three-game spell during another on-court coaching session after she squandered a lead in the final set.

Second seed Pliskova blew away an out-of-sorts Halep in the first set, the Czech losing just two service points after an aggressive start.

A forehand into the net put Halep a break down and Pliskova continued to return with vigour, toying with the Romanian as she took just 21 minutes to wrap up the set.

Halep heeded Cahill's advice by using more spin and taking pace of the ball as she broke in the opening game of the second set and showed character to edge a break up at 3-2 after Pliskova got back on serve.

Pliskova was unable to halt Halep's momentum and the fifth seed levelled the match with an ace before taking a 2-0 lead in the decider.

Yet Pliskova responded by winning five games in a row, peppering Halep with searing ground strokes and coming to the net at every opportunity.

Cahill's harsh words at 3-2 failed to prompt a positive reaction from Halep, and although she was able to get back on serve at 5-4, she was broken for the third time in the final set and bowed out when Pliskova had fortune with a netcord winner.

Defending champion Elina Svitolina earlier made it three wins out of three with a 7-5 7-6 (12-10) defeat of alternate Sofia Kenin and will take on Belinda Bencic for a place in the final.