Defending champion Elina Svitolina continued her dominance over world number two Karolina Pliskova with a straight-sets victory at the WTA Finals in China on Monday.

Opening Purple Group, the eighth seed started her title defence impressively with a 7-6 (14/12), 6-4 win in one hour and 53 minutes at the Shenzhen Bay Sports Centre.

It was Svitolina's fourth straight victory over a misfiring Pliskova who had 42 unforced errors.

"I was trying to be ready for her big serve and then take on the second serve," Svitolina said after the match. "The surface is a little bit slow and I had more ti... it benefited my return."

It was a disappointing result for Pliskova who started well, mixing trademark hard-hitting blows from the baseline with softer touch -- including an exquisite drop shot to capture a break in the first game.

But Svitolina slowly clawed her way back into the match and broke in the fourth game as Pliskova's radar went awry.

It was a tense contest extending into a nerve-jangling tiebreaker with Pliskova's bold approach saving six set points, but she miscued on the seventh as the Ukrainian finally drew first blood.

A frustrated Pliskova was broken immediately to open the second set and never seriously threatened to stage a comeback against an increasingly confident Svitolina.

The 25-year-old is hoping to end a barren season on a high having not captured a title since last year's WTA Finals triumph.

Pliskova, who has a tour-leading four titles this season, is making her fourth straight appearance at the round-robin tournament and has reached the semi-finals for the past two years.

US Open champion Bianca Andreescu takes on Wimbledon winner Simona Halep in the later match in a battle of the past two Grand Slam champions.