US Serena Williams (L)  and Australian Nick Kyrgios (R) of the Singapore Slammers play against Belgium's Kirsten Flipkens and Canadian Daniel Nestor of the Manila Mavericks  during their mixed doubles at the International Premier Tennis League (IPTL) competition in Singapore on December 2, 2014.  AFP PHOTO/ROSLAN RAHMAN        (Photo credit should read ROSLAN RAHMAN/AFP/Getty Images)