France though took the lead thanks Jo-Wilfried Tsonga's 6-3, 6-2 victory over John Isner in the men's singles.
Williams had to battle hard against Mathilde Johansson in the women's singles to square the score 1-1. She came back from a set down to beat the French woman 3-6, 7-5, 6-4.
Williams and Isner then joined hands and overcame Johansson and Tsonga in the mixed doubles to give the US the win. Williams/Isner beat Johansson/Tsonga 6-7 (5-7), 6-2, 10-8 (match tiebreak).
