Eugenie Bouchard of Canada in action against Ana Ivanovic of Serbia during a singles round robin match of the third day of the BNP Paribus WTA Finals 2014 at the Singapore Indoor Stadium, 22 October 2014. EPA/WALLACE WOON

Agnieszka Radwanska of Poland in action against Petra Kvitova of the Czech Republic during a singles round robin match of the second day of the BNP Paribas WTA Finals 2014 at the Singapore Indoor Stadium, 21 October 2014. EPA/WALLACE WOON

Ana Ivanovic of Serbia in action against Eugenie Bouchard of Canada during a singles round robin match of the third day of the BNP Paribus WTA Finals 2014 at the Singapore Indoor Stadium, 22 October 2014. EPA/WALLACE WOON

Serena Williams of the United States returns to Simona Halep of Romania during their singles match of the BNP Paribas WTA Finals 2014 at the Singapore Indoor Stadium, 22 October 2014. EPA/WALLACE WOON

Simona Halep of Romania reacts during her singles match against Serena Williams of the United States at the BNP Paribas WTA Finals 2014 at the Singapore Indoor Stadium, 22 October 2014. EPA/WALLACE WOON