The Brumbies gave Super Rugby champions the Chiefs their second defeat in as many weeks when they beat the Hamilton side 41-23 with a bonus point in Canberra.
The Chiefs now have have one win to show from their last six matches after winning their first three in a row.
The Brumbies outscored the Chiefs by five tries to two with doubles from Matt Toomua and Tevita Kuridrani.
The ANZAC Day match was a rematch of the 2013 Super Rugby Grand final in which the Chiefs beat the Brumbies 27-22 in Hamilton to secure their second Super Rugby title.
The Chiefs return home to Hamilton where they will host the Lions next week while the Brumbies travel to Christchurch to play a resurgent Crusaders team.
The Brumbies dominated the back-to-back champions to lead 36-9 after 63 minutes with 18 straight points while Chiefs replacement James Lowe was given a yellow card for tripping.
The Chiefs hit back with two late converted tries to reduce the final margin.
Try doubles to man-of-the-match Matt Toomua and centre Tevita Kuridrani helped sink the Chiefs, while winger Joe Tomane showed great hands to score in the corner.
The Brumbies closed to within one point of competition leaders the Sharks ahead of the Sharks match with the Highlanders in Durban later Friday.
The victory also increased the Brumbies' lead in the Australian conference to six points over the NSW Waratahs, who went down to the Blues in Auckland earlier Saturday.
The Chiefs have now only won twice in 11 trips to Canberra and the Brumbies lead 12-7 overall in their meetings.
The Chiefs attempted to run the ball early, dominating with 70 percent possession to take a 6-3 lead after 25 minutes.
Christian Lealiifano missed some kickable penalties early on before the Brumbies lifted their tempo and held on to the ball.
Fly-half Toomua burrowed his way over in the 30th minute and Lealiifano landed a penalty for a 13-6 lead at halftime.
Chiefs fly-half Gareth Anscombe kicked a penalty, but the Brumbies hit back through an acrobatic try in the corner to Tomane to lead 18-9.
The Chiefs launched a series of attacks but the Brumbies defence stood firm and when the New Zealanders looked certain to score Tomane swooped with an intercept and was only prevented from scoring when he was illegally tripped by Lowe.
The numerical disadvantage hurt the Chiefs, with Nic White slotting the ensuing long range penalty goal before Kuridrani's try double gave the Brumbies a 36-9 lead with 18 minutes remaining.
The Chiefs finished with tries to replacements Brad Weber and Josh Hohneck, but an intercept try to Toomua after the siren sunk any hopes of nabbing a bonus point.
"It's an outstanding result for us and we were after a really complete 80 minutes, so for us to do that tonight was really pleasing for the team," Brumbies captain Ben Mowen said.
"Hats off the backline guys because they were outstanding tonight, Matt Toomua at number 10 was really good."
Final Score Brumbies 41 (13) Chiefs 23 (6)
Tries - M.Toomua 2, J.Tomane, T.Kuridrani 2
Pen - C.Lealiifano 2, N.White 2
Con - C.Lealiifano, N.White
Tries - B.Weber, J.Hohneck
Pen - G.Anscombe 3
Con - A.Horrell 2
Cards - J.Lowe (yellow 52nd min)
Referee: Steve Walsh
Assistant Ref 1: Rohan Hoffmann
Assistant Ref 2: Andrew Lees
TMO: George Ayoub
1. Scott Sio , 2. Stephen Moore , 3. Ben Alexander , 4. Scott Fardy , 5. Sam Carter , 6. Jordan Smiler , 7. Jarrad Butler , 8. Ben Mowen (c) , 9. Nic White , 10. Matt Toomua , 11. Robbie Coleman , 12. Christian Lealiifano , 13. Tevita Kuridrani , 14. Joe Tomane , 15. Jesse Mogg
Replacements: 16. Siliva Siliva , 17. Ruan Smith , 18. JP Smith , 19. Jack Whetton , 20. Tom McVerry , 21. Michael Dowsett , 22. Andrew Smith , 23. Pat McCabe
1. Pauliasi Manu ,2. Mahonri Schwalger ,3. Ben Tameifuna ,4. Ross Filipo ,5. Brodie Retallick ,6. Nick Crosswell ,7. Sam Cane ,8. Liam Messam (c) ,9. Augustine Pulu ,10. Gareth Anscombe,11. Asaeli Tikoirotuma ,12. Bundee Aki,13. Andrew Horrell,14. Tim Nanai-Williams ,15. Tom Marshall
Replacements :16. Nathan Harris ,17. Jamie Mackintosh ,18. Josh Hohneck,19. Matt Symons ,20. Tevita Koloamatangi ,21. Brad Weber ,22. Dwayne Sweeney ,23. James Lowe