In Pictures: WTA Championships

Another player who started with an opening win over Kerber is Williams(***) rival for the title, world number one Victoria Azarenka (L). However, it took a set more for the Belarussian to defeat Kerber in their round robin match. Twice defeated Kerber is world number five

There was a premature end to the tournament for Czech Petra Kvitova. She retired after her opening defeat to Poland(***)s Agnieszka Radwanska. The defending champion told the media she was suffering from a viral illness

The woman to step in for Kvitova was none other than Australia(***)s Sam Stosur, the ninth top female player in the world. Stosur couldn(***)t get off to a winning start suffering a three-set defeat to Italian Sara Errani

Russian Maria Sharapova is not only hunting down the WTA Championships title but also the world number one ranking. The French Open winner has already made the semi-finals although current world number one Victoria Azarenka needs another win to get through

The woman standing in the way of Azarenka keeping her top spot is China(***)s Li Na. If Li Na defeats Azarenka she will take the last semi-final spot in the red group. And if Sharapova wins the tournament the world of tennis will have a new top dog

The final place in the white round robin group came down to an all or nothing clash between Poland(***)s Agnieszka Radwanska and Italy(***)s Sara Errani. The result followed form with the fourth seed Radwanska defeating her seventh ranked opponent to join Maria Sharapova in the semis

After her two-set victory over Azarenka, Serena Williams is unbeaten in the competition. The American is not competing for the world number one ranking as she hasn(***)t played enough tournaments this year. However, she consistently beats the seeds above her