Poland's Agnieszka Radwanska beat former Wimbledon champion Petra Kvitova in three sets to win her first WTA Finals title in Singapore.
The world number six came from a break down in the deciding set against her 25-year-old Czech opponent to win 6-2 4-6 6-3 in two hours and five minutes.
It was the 26-year-old's first final at the event in her seventh appearance.
World number five Kvitova had knocked out five-time Grand Slam winner Maria Sharapova in Saturday's semi-final.
A tearful Radwanska, the first woman to go on to lift the title after losing two round-robin group games, said: "It means everything to me, in my first final, I get my first win so it couldn't be any better.
"I was doing the right thing in the important moments of a really close match. I had my chances in the second set but it doesn't really matter how I won."