Their victory puts them firmly in the playoffs mix, while the Blues, who take a losing bonus point, drift further out of the reckoning with difficult home games against the Hurricanes and Chiefs to come over the next fortnight.
There is also the tricky task of a match against the Crusaders in Christchurch to come. It looked promising for the Blues after four consecutive victories, but their three losses since have really knocked the stuffing out of them.
After a good start at GIO Stadium in which they went to an early lead, the Blues had few attacking chances. In the second half, and despite a 15-12 lead, their backs were merely interested bystanders at times, the Brumbies going to their tried and tested tactic of the lineout drive which gifted their hooker Folau Fainga'a three tries.
It certainly wasn't pretty but it was all they needed to do after a very loose opening 10 minutes during which the Blues took a 12-0 lead thanks to TJ Faiane's try, the midfielder running a perfect line for Melani Nanai's assist, and Caleb Clarke's intercept of Christian Lealiifano's overly-ambitious wide pass.
The visitors were defending well and attacking with patience and, with the Brumbies losing big lock Rory Arnold to an ankle injury, it all seemed a little easy until the Brumbies turned the tables.
Monopolising possession and territory, they set about putting a huge amount of pressure on the Blues through a series of attacking scrums, and while the Blues survived those, albeit with a warning, prop James Slipper was soon over the line.
First-five Harry Plummer, hooker James Parsons and lock Patrick Tuipulotu entered the fray five minutes into the second half and while Tuipulotu and loose forward Dalton Papalii went on some useful charges, the game was all but done once Fainga'a scored his third try to allow his side to take the lead for the final time.
The Blues just couldn't wrest the initiative away from the home side, a familiar story for a side who haven't won away from Auckland this season.
"Some silly penalties and our set piece let us down," skipper Blake Gibson said afterwards.
"We were trying to fix what was going wrong on the go but it didn't quite work out. We just couldn't get back into the game."
Brumbies 26 (Folau Fainga'a 3, James Slipper tries; Christian Lealiifano 3 cons)
Blues 21 (TJ Faiane, Caleb Clarke tries; Otere Black con, pen, Harry Plummer 2 pens)
Halftime: 12-15