Dennis takes over from Stephen Hoiles on the side of the scrum after recovering from the knee injury that sidelined him from the win against the Reds two weeks ago.
But after two bonus point wins from two outings, Cheika has refused to make any further changes to the team.
“I think they have played well enough to deserve more opportunities,” he said.
“But there are a few players who are pressing hard from the bench as well. Sekope Kepu is doing very well, he’s pushing hard for his chance. Obviously it’s difficult for Stephen Hoiles because he had a very good game in the Queensland match but everyone understands their role in the team.”
In the tight five, the front row remains the same, whilst lock Jacques Potgieter’s robust display against the Reds has enabled him to keep his spot alongside Kane Douglas.
The backrow is now Dennis on the blindside, Michael Hooper at openside flanker and Wycliff Palu at No. 8.
Nick Phipps and Bernard Foley will wear nine and 10, while Kurtley Beale will continue to make his play for higher honours from the inside centre position.
Relishing his role at outside centre, Adam Ashley-Cooper provides the link between Beale and the back three of Alofa Alofa, Peter Betham and Israel Folau, which remains unchanged.
Australia’s best-performing franchise last season and playing at home, the Brumbies will be a real challenge. ,I’m not trying to take the underdog tag, it’s there by right,” said Cheika.
“The Brumbies have got a lot of experience, they were described in the commentary last week as very efficient and they certainly are that.
“They are best team in Australia, they were 15 minutes away from winning the Super Rugby competition last year and it’s up to us to take on the best and try and compete with them away from home.”
With the Waratahs’ ball in hand style and the Brumbies’ kick and containment, it will be a clash of two styles and a bit of a stand-off says Cheika.
“It’s a case of who blinks first. I think they know we counterattack they will try kick it long and pin us down there and wait for us to make a mistake. The question for us is do we try and not make a mistake or do we counter attack hard and play our best footy….I think you know what we are going to choose, so we’ll see how good we are.”
1. Benn Robinson (Eastwood) , 2. Tatafu Polota Nau , 3. Paddy Ryan , 4. Jacques Potgieter , 5. Kane Douglas , 6. Dave Dennis (c) , 7. Michael Hooper , 8. Wycliff Palu , 9. Nick Phipps , 10. Bernard Foley , 11. Peter Betham , 12. Kurtley Beale , 13. Adam Ashley-Cooper , 14. Alofa Alofa , 15. Israel Folau
Replacements from : 16. Tola Latu , 17. Jeremy Tilse , 18. Sekope Kepu , 19 Will Skelton , 20. Stephen Hoiles , 21. Pat McCutcheon , 22. Brendan McKibbin , 23. Rob Horne , 24. Matt Carraro , 25. Jonno Lance ,