Naomi Osaka extended her winning-streak to 11 matches after defeating Petra Kvitova of the Czech Republic 7-6 (1), 4-6, 6-4 in the first of three round-robin matches at this year's WTA Finals on Sunday.

Osaka, the Australian Open champion, arrived in Shenzen having won the last two tournaments she played - in Osaka, Japan, and Beijing.

The two-time Grand Slam champion failed to take advantage of two match points when serving at 5-2 in the third, but nailed down the victory on a third match point when serving in the 10th game.

Kvitova surrendered the encounter when she sailed a backhand crosscourt wide on the final point.

The only other time Osaka played Kvitova took place when the Japanese player captured this year's Australian Open final bu a score of 7-6 (2), 5-7, 6-4.

Osaka's debut at the year-end final last year in Singapore ended in disappointment when she lost all three of her round-robin encounters.

The 29-year-old Kvitova, the oldest player in this year's eight-player field, is competing in her seventh WTA Finals. She won the year-end title in her first appearance in 2011, and was also a finalist in 2015.

Osaka is now 1-0 and Kvitova 0-1 in Red Group round-robin action.

Top-ranked Ashleigh Barty of Australia and Belinda Bencic of Switzerland make their WTA Finals debuts playing each other in the next match on Sunday.

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