Defending champion Caroline Wozniacki beat Petra Kvitova at the WTA Finals in Singapore.
Denmark's Australian Open champion Wozniacki, 28, overcame a knee injury during the second set to win 7-5 3-6 6-2.
It is the first time she has beat Czech Republic’s Kvitova, 28, in four years – her last victory over the fourth seed also coming at the WTA finals in 2014.
The WTA Finals features the leading eight players this year, split into two groups of four.
The top two players from each round-robin group will progress to the semi-finals, with the final on 28 October.