The Bulls extended their winning streak over the Waratahs to seven consecutive matches when they beat the Waratahs 24-27 in Sydney.
The Waratahs have not beaten the Bulls since 2005 and have now lost their last three home matches against the former champions.
The Waratahs will now more than likely need to rely on other results going their way if they are to qualify for the play offs in July.
The Waratahs looked like they had done enough to end the streak with three minutes remaining as they were leading 24-20.
But the home side turned the ball over at a scrum five meters out from their own line.
Waratahs No. 8 Lopeti Timani picked the ball up off the back of the scrum and was forced back into his own in-goal by the Bulls.
From their ensuing scrum feed, the Bulls mauled and lock Werner Kruger crashed over the line. Morne Steyn converted all three Bulls tries and added two penalties.
The Waratahs led for most of the match but the Bulls' forward pack forced errors from the home side to get up in the final minutes.
The three-time Super 15 champions outscored the Waratahs three tries to two to put the Pretoria-based Bulls in good heart for their upcoming two-match tour to New Zealand.
Bulls' fly-half sharpshooter Morne Steyn kicked three conversions and two penalties in another immaculate goalkicking display.
The Waratahs struck early when returning Wallaby centre Rob Horne stormed on to a Berrick Barnes pass and outsprinted the defence in the 16th minute, before scrum-half Francois Hougaard levelled the scores eight minutes later.
Hougaard shrugged off tackles from Waratahs forwards Rocky Elsom and Benn Robinson to score, before Barnes kicked the home side in front at halftime 13-10 with a penalty.
The Bulls applied the pressure on the Waratahs' defence midway through the second half leading up to winger Akona Ndungane's try to pinch a 17-16 lead.
But the Waratahs hit back with a 63rd-minute try to winger Atieli Pakalani off a Barnes pass.
The Waratahs led 24-20 into the final minutes before Kruger barrelled his way over capitalising on an error from forward Lopeti Timani, who picked the ball up off the back of his scrum and was forced back into his own in-goal by the surging Bulls.
The Waratahs, who now risk being overtaken into second place by the Reds, who play the Chiefs at home on Sunday, face a difficult two-game tour to South Africa where they played the Stormers next weekend.
Final Score Waratahs 24 (13) Bulls 27 (10).
Tries - R. Horne, A. Pakalani
Pen - B. Barnes 3, B. McKibbin
Con - B. Barnes
Cards - D. Mumm (yellow)
Tries - F. Hougaard, A. Ndungane, W. Kruger
Pen - M. Steyn 2
Con - M. Steyn 3
Referee: Chris Pollock
Assistant Ref 1: Ian Smith
Assistant Ref 2: Francisco Pastrana
TMO : George Ayoub
15. Daniel Halangahu, 14. Tom Kingston, 13. Rob Horne, 12. Adam Ashley-Cooper, 11. Atieli Pakalani, 10. Berrick Barnes (vc), 9. Sarel Pretorius, 8. Wycliff Palu, 7. Chris Alcock, 6. Rocky Elsom (c),5. Kane Douglas, 4. Dean Mumm, 3. Sekope Kepu, 2. John Ulugia, 1. Benn Robinson .
Replacements: 16. John Mann-Rea, 17. Jeremy Tilse, 18. Sitaleki Timani, 19. Lopeti Timani, 20. Dave Dennis, 21. Brendan McKibbin, 22. Tom Carter.
15. Zane Kirchner, 14. Akona Ndungane, 13. Johann Sadie, 12. Francois Venter, 11. Bjorn Basson, 10. Morne Steyn, 9. Francois Hougaard, 8. Pierre Spies, 7. CJ Stander, 6. Deon Stegmann, 5. Juandre Kruger, 4. Flip van der Merwe, 3. Werner Kruger, 2. Chiliboy Ralepelle, 1. Dawie Steyn
Replacements: 16. Willie Wepener, 17. Rayno Gerber, 18. Wilhelm Steenkamp, 19. Arno Botha, 20. Jano Vermaak, 21. Louis Fouche, 22. JJ Engelbrecht.