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 five 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.
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)