The Brumbies have slumped to a fourth-straight Super Rugby loss, wasting their first-half dominance to be overcome 13-6 by the Lions in Canberra.
Friday night's match at GIO Stadium continued their drought against overseas opposition and made it the first time they had lost four on the bounce since 2011.
It comes as they prepare to embark on a tough world tour to play South Africa's Kings in Port Elizabeth and Jaguares in Buenos Aires.
The opening 25 minutes were played almost exclusively in the Brumbies' attacking half.
But after winger James Dargaville had a try disallowed in the opening stages, Wharenui Hawera's 18th-minute penalty goal was all they had to show as they went to the break leading 3-0.
While the Lions managed to get on the front foot a handful of times before the break, the Brumbies finished the half with 74 per territory and 63 per cent possession.
The Lions' game was littered with errors but their defensive guile allowed them to stay in the fight.
Elton Jantjies levelled the scores 10 minutes after the break, with a penalty goal the first sequence of a game-changing one-two punch.
Brumbies fullback Aidan Toua threw a wild pass, which was pounced on by Lions centre Lionel Mapoe who gave the offload to flanker Kwagga Smith.
The former sevens' star showed an electrifying turn of pace to run more than 60 metres and score the only try of the match.
Jantjies added the points to give the visitors a 10-3 lead.
With the game opening up, Lions winger Courtnal Skosan gave away a penalty for not releasing the ball, allowing Hawera an easy shot to shave the deficit to four.
But despite halfback Joe Powell twice breaching the Lions' line, the Brumbies were kept tryless for a second consecutive game.
An offside penalty in the dying minutes gave Lions fullback Andries Coetzee the chance to put the icing on the cake with the final kick of the match.
The victory cemented the Lions at the top of the South African conference with their seventh-straight win, boosting their record to 10-1.