At the 2013 Hopman Cup, and playing for USA (with John Isner), the first rubber was against South Africa. Williams beat Chanelle Scheepers and, with John Isner, they comfortably defeated the South African pair Chanelle Scheepers and Kevin Anderson. In USA's second rubber against France, she won both her singles and in mixed doubles defeated Jo-Wilfried Tsonga and Mathilde Johansson. Next she faced Anabel Medina Garrigues of Spain and won in two sets.