Three players will be fighting to be World No1 after Caroline Wozniacki stumbled out of the Australian Open yesterday.
The Dane fell to defending champion Kim Clijsters and, as a result, will have to surrender top spot.
Russian Maria Sharapova, Czech Petra Kvitova and Victoria Azarenka of Belarus are in contention to inherit the prized position.
Clijsters' 6-3, 7-6 (7-4) victory over Wozniacki propelled her into a semifinal showdown with Azarenka.
The third seed had earlier scraped past Pole Agnieszka Radwanska in three sets, 6-7 (0-7), 6-0, 6-2.