China's Li Na reached the final of the WTA championshipsin Istanbul after beating Czech Petra Kvitova in straight sets.
Li Na overpowered back-injury victim Victoria Azarenka 6-2 6-1 to power through to the semi-finals at the WTA Championships.
Round-robin formats at tennis tournaments can cause confusion but Serena Williams has an easy solution, just keep winning.
Serena Williams cruised to a straight sets 6-2 6-4 win against Agnieszka Radwanska at the WTA Championships.
Serena Williams showed her desire to defend her WTA Championships title by sweeping to a 6-3 6-1 win over Angelique Kerber.
Serena Williams aims to claim her 11th tournament trophy to round off one of the best years of her career.
Angelique Kerber has clinched the final spot at the WTA's season-ending championships after reaching the Linz Open semis.
WTA rankings on Monday (Last week's positions in brackets):
Maria Sharapova has withdrawn from the season-ending WTA Championships in Istanbul due to a shoulder injury.
Serena Williams and Jelena Jankovic set up a final showdown in the China Open after contrasting victories in the semi-finals.
Serena Williams overcame the sixth seed Caroline Wozniacki 6-1 6-4 to progress to the semi-final of the China Open.
ATP World Tour Finals
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