The NSW Waratahs have a chance to overtake them with a big win over the Cheetahs at Allianz Stadium on Saturday.
Both the Rebels - whom the Brumbies play next week at AAMI Park - and Tahs, however, have a game in hand.
While the ACT club were without inside centre Matt Toomua, who will be out for six weeks after having surgery on his knee, they welcomed back inspirational Wallabies skipper Stephen Moore.
It was, as expected, a brutal battle with the Bulls and their massive forward pack - and it showed in the opening exchanges, with the home side looking a little off especially at the scrum.
The Pretoria-based Bulls were first on the board via a penalty goal in the fourth minute, but three off the boot to Christian Lealiifano gave the Brumbies a 9-3 lead at halftime.
Similarly to last week, Stephen Larkham's men enjoyed a large share of possession but couldn't put the finishing touches on a handful of attacking opportunities in the first half.
The break proved helpful, though, with Nigel Ah Wong and Tomas Cubelli scoring the game's only tries in the 45th and 57th minutes respectively - both converted by Lealiifano.
The 17-point win was their biggest over the Bulls since 2003.
Larkham said it was pleasing to finally get a reward after weeks of effort.
"I don't think we've been in a hole, I think the boys have been playing really well," he said.
"The effort, the attitude and the will to go out there and play well has been spot on the last couple weeks, tonight we just got the result.
"It's getting to that point where the season's pretty tense for us but it really paid off tonight."
Bulls coach Nollis Marais said mistakes and penalties (14-9 against them) cost them the game.
"We made it easy for the Brumbies to defend and all credit to them, they took advantage of it," he said.
He said the breakdown had been a big concern against David Pocock, who was dominant despite having only one steal.
"He got a vital steal in their 22, but I just think it was a good effort from the Brumbies - they came up and out our whole line under pressure."
The Bulls play the Waratahs in Sydney next week.
- AAP