US Open champion Sam Stosur has defeated Maria Sharapova in their opening White Group game of the end-of-season WTA Championships in Istanbul.
The 27-year-old Aussie eased past the former Wimbledon champion 6-1 7-5.
After a dominant display in the opening set Stosur held off an improved Sharapova to triumph in two sets.
In the Red Group there were wins for world number one Caroline Wozniacki and Wimbledon champion Petra Kvitova.
