Serena Williams retained her WTA Championships title on Sunday with a 2-6, 6-3, 6-0 win over China's Li Na.

It was the world number one’s 78th win and 11th title of 2013.

“I can't believe I won, I was so tired. Did I really win? It’s really awesome; it’s such a special moment,” said the 32-year-old.

Serena Williams overcame physical problems as well as emotional distress to defeat Jelena Jankovic 6-4, 2-6, 6-4 on Saturday and reach the WTA championships final.

The world No. 1 and defending champion put in a stumbling performance and twice sat weeping into her towel during change-overs. She also committed 40 unforced errors and hit 40 winners, and allowed a 5-1 final set lead to evaporate to within one point of 5-5 before finishing the match with three trademark heavy blows.

Meanwhile, Jankovic has said that Serena Williams always throws tantrums whenever she starts losing, and that it is something that as a player you have to pay attention to, which is distracting.

According to The Age, Williams, who claims to be exhausted near the end of a long season, reacted with fretful worrying, and sometimes distracting behaviour while struggling to beat Jankovic.

It included weeping into her towel, gesticulating and arm-waving, bending over and slumping, yelling and calling out, and conducting the game at different speeds, the report said. She said of Williams’ go-slow moments that she never saw her do this when she was leading, adding that it was not the first time when they played that she was doing this and it was her way of playing.

Nothing in the rules of tennis says a player shall not play at different speeds, the report added.

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