Roberts, 23, said: "It was a huge win for Scottish rugby and the weather conditions suited them down to the ground. But that result will make it tougher for us. It's always harder to play a side who have just lost.
"Australia will come here like a wounded animal and play with extra fire. It's a challenge we are looking forward to."
After a Shane Williams-inspired 33-16 win over Argentina, head coach Warren Gatland has also admitted his side need to raise their game for the showdown with Robbie Deans' men at the Millennium Stadium.
Gatland said: "We will definitely have to step up a level next week. Last year we beat Australia and we deserved the victory. But, having dealt with Australians before, I know they will be smarting from that defeat. It will make them even more determined to win.
"It will be nice to show another level of work in training and in our performance next weekend to make sure we improve from game to game."