To be named on Thursday morning, it will be the first time in his 26-match reign he hasn't made a change to the starting 15, having made at least four in every Test so far this year, many forced by injury.
It means Rennie is backing in the same personnel to tidy up some significant flaws from the 25-17 Rugby Championship win against the Springboks in Adelaide last weekend, including deficient set-piece work that saw them win just seven of their 13 lineouts.
He'll again go with an all-Brumbies front row of James Slipper, Folau Fainga'a and Allan Alaalatoa over bench options Taniel Tupou, Scott Sio and Dave Porecki, while outside back Andrew Kellaway will again have to make his impact off the pine.
South Africa coach Jacques Nienaber has taken the opposite approach, swinging the axe with nine changes to his injury-hit team.
Notably, five-eighth Handre Pollard misses with a knee injury and will be replaced in the No.10 shirt by Damian Willemse, whose fullback role will be taken by veteran Willie le Roux.
Wallabies assistant coach Scott Wisemantel called on the team to be more ruthless in delivering a complete display, having coughed up a bonus point in allowing two late tries in the Adelaide Test.
"You're filthy that you miss that point, you're absolutely livid," he said.
"We're really disappointed with that last eight-to-10-minute period, and we had chances there, even when it was three tries to one we had another chance off a set piece to do something.
"We've got to be a little bit more cut-throat, a little bit more ruthless in that regard, so it's definitely something we've spoken about and we've worked on."
