The Brumbies had Darcy Swain and Luke Reimer sin-binned as they chaotically clung to a 16-12 lead at the death on Saturday night.

They'd already had Rob Valetini in the bin for 10 minutes earlier in the second half while the final 10 minutes left Brumbies coach Dan McKellar later biting his tongue about the officiating.

His men repelled two scrums with just six in the line-up then incredibly stopped a rampaging Taniela Tupou from a close-range quick tap, before the Reds finally spread it and O'Connor slid over to the delight of 41,637 fans.

O'Connor's well-documented transformation from teenage troublemaker to 30-year-old leader continued as he scored all 19 of the Reds' points.

"I'm pretty blown away, it's a surreal moment," O'Connor said.

"We are our worst enemies at times but when the game's on the line (we find a way)."

Incredibly, their third comeback win against the Brumbies came despite them leading for just 23 minutes across all three games.

It's the Reds' first silverware since they beat the Crusaders for their only Super Rugby title 10 years ago and is a changing of the guard for Australian rugby after the Brumbies beat them in a tight decider in Canberra last year.

The Brumbies controlled the first half, forcing the Reds to make 75 tackles to their 38 as the hosts coughed up possession and failed to find yardage with kicks or any punch with ball in hand.

A Tom Banks try was the only five-pointer to show for it though, the Reds being denied a reply when Feao Fotuaika was judged to have been held up as he scrambled through feet and jerseys to eventually find the in-goal area.

Penalties kept the Reds close while the Brumbies found three-pointers of their own, targeting winger Jordan Petaia with their kick-offs and daring him to kick.

The worm looked to have turned when Valetini was sin-binned for a tackle that slipped up on Jock Campbell's chin in the 60th minute.

But the teams only traded penalties in that period, the Reds instead flicking the switch with five minutes to go when they opted to scrum directly in front.

Player-of-the-match Fraser McReight led the charge, signalling to the crowd for support, and they lifted in an intense final 10 minutes that at one stage saw almost all of the 13 remaining Brumbies piling behind the ball under the posts to defend their line.

Penalties ended 20-8 in favour of the Reds, McKellar again quizzing that count and wondering how some of the late penalties were blown by referee Nic Berry.

"When we held the guy up, there was no advantage, then there was penalty so that's another crack," he said.

"Just shattered, gutted, proud but at the same time not a lot to say.

"Heartbreaking ... I thought they were brilliant. Backs to the wall, a lot of injuries out of last week and we're shattered.

"Just as long as everyone's accountable for their performance out there tonight."

Australia's two stand-out sides will now lead the country's charge in the Trans-Tasman competition that begins next week.

Australian Associated Press