The Blues' 21-19 win - a club record 12th straight - moved them further ahead on top of the ladder and likely relegated the Brumbies to third place with one round to play.

The Brumbies, despite being camped in their own half defending for a bulk of the game, went ahead by one when Billy Pollard's try was cooly converted by Noah Lolesio with 70 seconds to play.

They won the ball from the restart but lost possession and then watched as the visitors worked towards the posts, winning a penalty despite protests from the hosts.

Under advantage, All Blacks playmaker Barrett calmly slotted the winner to end what had shaped as another feel-good story for Australian rugby.

The Brumbies were furious at a penalty count 16-5 in the Blues' favour and at one point had made 95 tackles to the Blues' 38.

"We showed so much heart tonight; our backs were against the wall through the whole game," captain Allan Alaalatoa said.

"I think some of those were our fault, but mate I reckon we'll get an apology later in the week, some videos (reviewing the penalties).

"We defended our hearts out and I just don't feel we were getting the rub of the green ... but we still managed to be up in the 79th minute."

With the Crusaders five points clear in second, the Brumbies look likely to miss the chance of a home semi-final, instead now needing a win over Moana Pasifika to secure third ahead of the surging Chiefs.

"That was almost Test match intensity with the young packs and see-saw nature of the game," Barrett said.

"When you come to Canberra you're up for a hell of a fight and we certainly got that."

The hosts had shot out of the blocks and led 7-0 after Pete Samu found a patch of grass to plant the ball in the second minute.

But it was all the Blues after that, the Auckland outfit applying immense pressure as they threatened to reply.

But it remained that way for almost 40 minutes, Roger Tuivasa-Sheck one of three would-be Blues scorers held up over the line and Kurt Ekland's try overruled for a knock-on.

Folau Fainga'a and Darcy Swain were sin-binned as a 12-1 penalty count took its toll, but still they held firm until Barrett crossed for a try off a scrum after the halftime siren.

Brumbies halfback Nic White broke that momentum with a sharp intercept at the resumption, running 80 metres before Fainga'a scored soon after from a maul to put the hosts back in front.

Blues winger Caleb Clarke limped off with a hamstring injury but Karl Tu'inukuafe's try and another penalty gave the Blues a six-point lead inside the final five minutes.

Pollard scored his late try off a trademark Brumbies lineout and maul and Lolesio snuck his conversion inside the right post to put them up by one with just over a minute to play, before the Blues pulled off their great escape.

Australian Associated Press