Karolina Pliskova took another step towards the WTA Finals by reaching the last eight of the Tianjin Open with an emphatic straight-sets win over Polona Hercog.

Pliskova occupies the eighth and final qualification spot for the season-ending tournament and must reach the semi-finals this week to add to her points haul.

The top seed looked in good shape to take one of the three remaining places in the Singapore showpiece as she eased to a 6-1 6-2 victory over Hercog on Wednesday.

Former world number one Pliskova won 80 per cent of points behind her powerful first serve and was not broken in a one-sided match, setting up an encounter with Katie Boulter or Barbora Krejcikova.

Aryna Sabalenka still has an outside chance of making a WTA Finals debut this month and maintained her excellent form with a 6-1 6-3 defeat of Magda Linette.

Fourth seed Sabalenka, beaten by Maria Sharapova in the Tianjin final last year, will come up against Timea Bacsinszky or Misaki Doi in the quarter-finals after breaking five times to cruise through.

Petra Martic battled back to see off Fangzhou Liu 1-6 6-0 6-1, while Hsieh Su-wei needed three sets to topple Veronika Kudermetova 6-2 2-6 6-2.