USA's Serena Williams, with her nails painted in the colors of the US flag, holds her racket during her women's first round singles tennis match against Australia's Daria Gavrilova at the Olympic Tennis Centre of the Rio 2016 Olympic Games in Rio de Janeiro on August 7, 2016. / AFP / Roberto SCHMIDT (Photo credit should read ROBERTO SCHMIDT/AFP/Getty Images)

USA's Serena Williams, with her nails painted in the colors of the US flag, holds her racket during her women's first round singles tennis match against Australia's Daria Gavrilova at the Olympic Tennis Centre of the Rio 2016 Olympic Games in Rio de Janeiro on August 7, 2016. / AFP / Roberto SCHMIDT        (Photo credit should read ROBERTO SCHMIDT/AFP/Getty Images)