Defending champion Elina Svitolina continued her dominance over world No 2 Karolina Pliskova with a straight-sets victory at the WTA Finals in China on Monday. Opening the Purple Group, the eighth seed started her title defence with a 7-6, 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. "The surface is a little bit slow and I had more time ... it benefited my return. "It's a big privilege to return to this event. I still can't believe I won it last year." 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. 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. In yesterday's opening matches over in the Red Group, Naomi Osaka eventually overcame Petra Kvitova 7-6, 4-6, 6-4 in a marathon battle that lasted two hours 39 minutes, while Ashleigh Barty recovered from losing the opening set to beat Belinda Bencic 5-7, 6-1, 6-2.