The Crusaders, meanwhile, need to rebound quickly with a grand-final rematch against the unbeaten Chiefs in Hamilton.
The home side held an early 14-7 lead courtesy of tries to David Havili and George Bell but the Brumbies struck twice in the 10 minutes before halftime to take a 19-14 lead into the break.
The key moment of the match was a classic bounce of the rugby ball, after Declan Meredith kicked into the Crusaders territory, with the bounce splitting two Crusaders players and getting into the hands of Kadin Pritchard, who ran clear to score, putting the Brumbies 10 points clear.
The Crusaders closed the margin through Sevu Reece in the 57th minute to make it 24-19 but the unwavering Brumbies struck straight back when Charlie Cale went over for his second try. To make matters worse, Dom Gardiner was yellow-carded for a high shot in the build-up, leaving the Crusaders down a man chasing a 12-point deficit.
The defending champions gave themselves a chance of a comeback when Leicester Faingaʻanuku beat two tackles to score down the left – making it 31-24 with 12 minutes to play. But it was all Brumbies in the final 10 with Liam Bowron, Rob Valetini and Corey Toole all crossing the chalk.
The Crusaders only have two more games at Apollo Projects Stadium but the old ground wouldn’t have seen too many home thrashings like that.
Crusaders coach Rob Penney labelled the final quarter “embarrassing”.
“Well it was pretty brutal. Again, we started off, created a little bit, then just made errors. So we just lack a little bit of cohesion, or quite a bit of cohesion. And the Brumbies just grew on the back of that and, you know, the last 20 was embarrassing, wasn’t it? he told Newstalk ZB.
Penney said the handling errors, which was also an issue in the defeat to the Highlanders, was something the players have been working on.
“They’ll be the first ones looking in the mirror, they’ll be really disappointed with themselves. We’re doing a lot of handling at training and under pressure, so doing all what you’d regard as the right things to try to set ourselves up, but something’s just not quite right at the moment,” he added.