Hewitt wins, Serena Williams pulls out

Lleyton Hewitt's hopes of landing a long-awaited Hopman Cup trophy remain alive after Australia Gold secured a 3-0 victory over the US in Tuesday night's tie at Perth Arena.

Australia were guaranteed the tie win after world No.1 Serena Williams retired hurt from her singles match against Jarmila Wolfe.

Williams was trailing 7-5 2-1 when she called it quits because of an ongoing left knee injury, with her retirement handing Australia Gold victory in both the women's singles and doubles rubbers.

Hewitt, who will retire after the Australian Open later this month, then beat Jack Sock 7-5 6-4 to make it a 3-0 sweep.

Australia Gold will reach the Hopman Cup final if they can beat the undefeated Ukraine on Thursday.

Hewitt has slid to 307th in the world rankings after focusing his attention on managing his body during the twilight of his career.

But the two-time grand slam winner was still far too good for world No.26 Sock, with the American lacking the competitive grunt of Hewitt.

Hewitt is appearing at his eighth Hopman Cup, but he is yet to taste trophy success.