The Brumbies have surrendered top spot in the Australian conference after going down 44-23 overnight in Pretoria.
The result kept the Brumbies winless on their two-game trip to South Africa.
The Brumbies were never in the game as the Bulls run out to a 31-6 lead by the 44th minute.
“The Bulls put on a display tonight they were impressive right around the park and deserved the win,” Captain Ben Mowen said.
The Brumbies return home for a must win match against the Rebels on Saturday 31 May.
10 Brumbies are then involved in the Wallabies three Test series against France throughout June.
They then return to face a in-form Waratahs at ANZ Stadium on 28 June.