Result: Maria Sharapova slumps to second defeat

Former world number one Maria Sharapova has suffered her second defeat at the WTA Championships after losing in straight sets to Li Na this evening.

The 24-year-old put up a stern challenge during the opening set, although French Open champion Na eventually prospered 7-4 on a tie-break.

The second set would prove to be more straightforward for Na, breaking Russian-born Sharapova on two occasions to record a 7-6 6-4 victory in Istanbul.

Yesterday Sharapova was defeated by US Open champion Sam Stosur.

Sharapova can no longer qualify for the semi-finals of the tournament as a result of today's loss.