Belgian world number two Clijsters quit after hurting her left ankle while leading Hewitt's Australian team mate Alicia Molik 6-3 6-7 3-2 in the opening singles. A scan revealed she had bruising on her ankle bone which later forced her to withdrew from the tournament.
The injury casts a shadow over her hopes for the upcoming Australian Open with medical experts only prepared to say they were "cautiously optimistic" she would be fit in time for the January 19 start of the Grand Slam.
Hewitt followed Clijsters onto court at the Burswood Dome and recovered from a loose first set to beat her Belgian team mate Xavier Malisse 3-6 6-1 6-2.
In an ironic twist, Hewitt also needed treatment after turning his left ankle in the third set of his match, but after applying additional strapping he continued and completed the victory.
"I was lucky I was wearing my ankle braces otherwise I'd be out of the whole Australian summer I guess," Hewitt said as he left the court. "It felt weak after it but I was alright."
With Clijsters unable to take part in the eagerly-anticipated "love match" mixed doubles against her fiancé, Australia were handed a 3-0 victory.
"PRETTY DISTRESSED"
"I saw Kim afterwards and she was pretty distressed," Hewitt said. "I guess she will just be hoping she can make the Australian Open later this month."
The win and Clijsters' withdrawal from the event puts Australia into Saturday's final of the A$1 million ($772,000) ITF mixed team competition.
They look likely to face the US in a repeat of last year's final after the Americans saw off France.
In the first match of the evening session, Lindsay Davenport belied her claims of being "underdone" entering the season when she beat world number four Amelie Mauresmo 6-4 6-4.
Having said she was "many matches away from really feeling great" after recovering from foot surgery, the American wasted no time taking apart her French opponent to give the U.S. a 1-0 lead.
"That was much better," she said. "I wasn't really expecting to win these matches so this is great."
James Blake then gave his side an unbeatable 2-0 lead when he sailed past Fabrice Santoro 6-3 6-4 before the American team clinched the mixed doubles 7-5 6-1 for a clean sweep.
"I don't know if it is losing the hair or the clothes but whatever it is, it's great," said Blake who lost his luggage on the trip over and who is sporting a new, closely-cropped hairstyle.
