"We'll move on from the disappointment of the weekend. [Australia] is a massive game for us," said Roberts.
"It would be disappointing to lose to Australia and go home having lost two games on the bounce, so we certainly want to win.
"[We have] a point to prove to everyone back home. A true test of character is how you react."
Asked whether the sending off of captain Sam Warburton in Saturday's game was a "sporting injustice", Roberts told BBC Sport: "It didn't help. We played as good a brand of rugby as you can play with 14 men on the pitch and we had chances to win it, and that makes losing all the more painful really."
Wales coach Warren Gatland has now revealed that he considered having one of his props feign an injury against France to force uncontested scrums following Warburton's dismissal and a calf injury to Adam Jones.