The Queensland Reds handed the Chiefs their first defeat in 11 matches this season to open round 12 in New Plymouth on Friday night, the stunning 25-22 win their first in New Zealand for a decade.
The Brumbies had to dig deep to avoid another upset in the final match of the weekend against the lowly Highlanders but hit the front for good in the 66th minute after a brilliant individual try from winger Corey Toole.
Number eight Pete Samu matched Toole with his second try of the match two minutes from time to secure the bonus point and send the Canberra club four points clear of the Wellington Hurricanes and Canterbury Crusaders.
"It was good to see the Reds step up there and beat the Chiefs, that certainly helps us in terms of where we can finish on the ladder, but we're not getting ahead of ourselves," said Brumbies coach Stephen Larkham.
The reigning champion Crusaders sent out a warning to the rest of the competition that they are hitting their formidable stride by grinding out a 15-3 over the Auckland Blues on Saturday night in a blockbuster rematch of last year's final.
Lock Quinten Strange and winger Leicester Fainga'anuku scored the only tries of a defence-dominated contest in Christchurch, and the Blues played for 20 minutes with 14 men after their skipper Dalton Papali'i was red-carded.
"To hold them to three points was a huge testament," Crusaders captain Scott Barrett said.
"At times it was probably a bit ugly, and we didn't fire too many shots, but we closed down their game and a lot of their firepower didn't get into it."
Earlier in the New Zealand capital, All Blacks loose forward Ardie Savea scored three second-half tries as the Wellington Hurricanes bounced back from last week's shock loss to Fijian Drua with a 71-22 thrashing of the winless Moana Pasifika.
With three rounds of the regular season remaining, the high-scoring Hurricanes lead the Crusaders on points difference with the Blues a further three competition points back in fifth place.
The New South Wales Waratahs in sixth place cut the gap to the leading pack to eight points with their third successive win after prevailing 38-20 in a hard-fought contest with the Melbourne Rebels on Saturday.
The Drua came back to earth with a bump on Friday after the more than 6,000-km (3,700-mile) journey from Suva to Perth as Western Force scored three tries and kept the visitors scoreless after halftime for a 34-14 win.
The victory saw the Force leapfrog the Drua into eighth place, the last slot that earns a team a place in post-season play.