Venus Williams still has a lot of work ahead to recapture the form that has made her a seven-time Grand Slam champion.

After joining her sister Serena in a fourth-round Wimbledon exit, Williams lost in singles and doubles before helping the Washington Kastles to a 21-18 World Team Tennis over-time victory on Tuesday over reigning champion Kansas City.

Williams, 34th in the WTA rankings, lost 5-4 to 66th-ranked Christina McHale in a one-set singles matchup of the No 2 and 3 Americans and fell 5-1 in doubles alongside Australian Rennae Stubbs against McHale and Madison Brengle.

But Williams, showing no sign of the hip injury that sidelined her from the Australian Open until just before Wimbledon, joined India's Leander Paes for a 5-3 mixed doubles triumph and hit two over-time forehand winners on the deciding points.

"I feel good about my game. Me being here means I'm healthy enough to play," Williams said.

"I have just been relaxing, taking it easy. It's time to gear up and get myself started again. This is how I've started my summers for several years and I'm excited to be out here again."

Venus Williams, a five-time Wimbledon champion who also won the 2000 and 2001 US Opens, has not won a Grand Slam title since 2008 at Wimbledon, but she vows that at 31 she is far from finished as a force in women's tennis.