The Highlanders scored an 83rd-minute converted try to snatch a dramatic one-point win in Canberra on Saturday night.
The Brumbies looked set for their third victory of the season — and their 11th in a row at GIO Stadium — when hooker Folau Fainga'a scored his hat-trick try from a rolling maul in the 68th minute.
But the Highlanders applied intense pressure inside the Brumbies 22 with time up, forcing four penalties and the sin-binning of lock Murray Douglas.
That pressure was converted into a try by Te Ariki Ben-Nicholas, who drove over near the posts, and then Josh Ioane added the conversion which gave the Southerners their first win of the Super Rugby season.
Victory continued an impressive winning run over the Brumbies for the Highlanders, who have now beaten the Australian side in their last five encounters, including three in Canberra dating back to 2016.
Fainga'a gave the Brumbies a handy 12-3 advantage after half an hour with his two tries, taking his season tally to five already.
But the Highlanders took a 13-12 lead into halftime, thanks to a Jona Nareki try from a chargedown, with Ioane adding the conversion and a penalty just before the break.
That proved a precursor to the dramatic finish as the Highlanders snatched a morale-boosting win after being outclassed 42-20 by the Sharks at home in their first game of the season last weekend.
"After starting the way we did last week, to get a win like that, on the road, it's massive for us," said Highlanders halfback Aaron Smith. "To nail those lineouts and to do a simple strike of a phase play to score at the end, there'll be a lot of relief and it will make that long trip home a little bit easier."
Highlanders skipper James Lentjes was proud of his team.
"We've got a tough game next week against the Crusaders, so for us to come over here — they'd won 10 in a row — and get the points, we're bloody happy," said Lentjes.
Highlanders 23 (Jona Nareki, Te Ariki Ben-Nicholas tries; Josh Ioane 2 con, 3 pen)
Brumbies 22 (Folau Fainga'a 3 tries; Ryan Lonergan con, pen; Noah Lolesio con)