The Wallabies will unleash tenacious flanker Sean McMahon on an injury-ravaged Wales as they go into Saturday's World Cup shootout with top spot in Pool A on the line.
In the only change not forced by injury or suspension, lock Dean Mumm joins Kane Douglas in the Wallabies' second-row with Rob Simmons dropped.
Joining him in the starting XV is winger Drew Mitchell, Australia's most prolific World Cup tryscorer with 12, who takes the left wing spot from the injured Rob Horne (shoulder).
Star backs Israel Folau and Matt Giteau have overcome ankle and rib injuries respectively to be named.
Coach Michael Cheika has made it clear throughout the tournament how impressed he is with young McMahon - who has won man-of-the-match honours in his past two games, against Uruguay a fortnight ago and the USA in a pre-World Cup warm-up clash.
McMahon's selection also minimises the selection shake-up for the Wallabies - had Cheika gone with McCalman, it would've likely forced David Pocock out of the number eight jersey.
While the openside flanker role is Pocock's preferred position, he's grown immensely in the number eight role and will certainly end up back there when Hooper returns from his one-game ban in time for the quarter-finals.
Wales have deployed a starting backrow that includes their own ball-hunting duo of Sam Warburton and Justin Tipuric to counter the Wallabies' fearsome backrow.
"Tipuric is a fantastic player," Cheika said.
"We respect their players massively and we have to make sure we isolate and try to get onto our ball."
The Wallabies intend to use the Wales clash to further refine their approach before the knock-out games.
"Every match in this tournament has required our team to step up to another level and we'll need to do that again against an undefeated Welsh team," Cheika said.
"Every player in our squad knows the improvements required, and we still have two days to continue to make them, both individually and as a team.
"Saturday night at Twickenham is another opportunity for us to put in a solid performance and continue to build towards the next stage of the tournament."