The powerhouse Brumbies forward will provide the second-half punch as the ACT chases a victory against bitter rival the Waratahs at ANZ Stadium on Saturday night.

But had his life panned out how he thought, Auelua would have been in sky blue alongside one of the players he looks up to most - Wycliff Palu - instead of trying to run over the Waratahs' No.8. Auelua was one of the most talented junior forwards in Sydney when he burst into the Waratahs academy in 2006.

He worked with Palu to improve his game but decided moving to France was best for his career instead of chasing Super Rugby dreams. Now Auelua's back and he's lining up for the enemy in his second season in Canberra.

''Things happen for a reason. I enjoyed my time [at the Waratahs], but they had a lot of depth and great back-rowers,'' Auelua said.

''I stepped back a bit last year and realised I used to be a part of [the Waratahs set-up], but now I feel more at home in Canberra. Now it's just another game against the Tahs.

''Cliffy [Palu] was already a Wallaby when I was coming through … they had great depth. I was still in awe of a few of the guys around. I really admire Cliffy and still look up to him.''

Auelua will shift to the Brumbies bench for the massive Australian derby.

Scott Fardy returns to the second row after an ankle injury which kept him on the sidelines for two months, moving Peter Kimlin to blindside flanker and turning Auelua into a dangerous man on the bench.

Auelua was included in a Wallabies' logistics camp last month in preparation for the British and Irish Lions series.

The 29-year-old has forced his way into Test contention with his power running and his brutal hits in defence.

But he'll have limited game time to impress Wallabies coach Robbie Deans, with the Brumbies opting for tall timber to start the game and a late injection of Auelua's power.

''I won't be looking too far ahead, I'm just concentrating on what's happening at the Brumbies,'' Auelua said.

''We're playing good rugby and that's giving guys an opportunity to chase higher honours. I'm not losing focus, there's no doubt this game will be a massive one and, as a team, we need to try to keep that first spot [on the ladder].''

The Brumbies' forward pack performance will be crucial to securing victory.

All eight of the Waratahs' starting forwards boast international experience. The Brumbies have just five Wallabies in their starting XV.

''We have to make sure every moment counts because we don't know which moment is the big one,'' Brumbies coach Jake White said.