Flavia Pennetta of Italy in action against Agnieszka Radwanska of Poland during a match in round three of the singles round robin stage of the BNP Paribas WTA Finals 2015 held at the indoor stadium in Singapore, 27 October 2015. EPA/WALLACE WOON

Maria Sharapova of Russia in action against Simona Halep of Romania during their fourth round match of the singles round robin stage at the BNP Paribas WTA Finals 2015 tennis tournament in Singapore, 27 October 2015. EPA/WALLACE WOON

Simona Halep of Romania in action against Maria Sharapova of Russia during their fourth round match of the singles round robin stage at the BNP Paribas WTA Finals 2015 tennis tournament in Singapore, 27 October 2015. EPA/WALLACE WOON

Flavia Pennetta of Italy celebrates after beating Agnieszka Radwanska of Poland in their fourth round match of the BNP Paribas WTA Finals 2015 tennis tournament in Singapore, 27 October 2015. EPA/WALLACE WOON

Simona Halep of Romania in action against Maria Sharapova of Russia during their fourth round match of the singles round robin stage at the BNP Paribas WTA Finals 2015 tennis tournament in Singapore, 27 October 2015. EPA/WALLACE WOON