The Bulls slumped to their third Super Rugby defeat in a row after losing 26-21 in Perth to the Western Force on Saturday.
The defending champs outscored their hosts two tries to one, but six penalties from Force centre James O'Connor proved to be the killer blow for Victor Matfield's men, whose title ambitions took another turn for the worst.
That's five from nine games that the Bulls have failed to win thus far in 2011, whilst the Force have won their last two on the trot - and their first at home this season - to move off the bottom of the Australian conference.
Bulls fly-half Morne Steyn slotted a conversion and three penalties - his last securing a losing bonus point for his team, but the three-time Super Rugby winners still remain seven points outside the top six.
O'Connor got the home side on the scoreboard first, but the Bulls were celebrating their first try of the match after hooker Chiliboy Ralepelle powered over from close-range in the 11th minute.
The five points was just reward having been denied an earlier try to Bjorn Basson that was brought back for a forward pass.
O'Connor quickly responded with another three-pointer from the tee, but was sent to the bin just second later Just seconds later for a dangerous tackle on Bulls full-back Zane Kirchner.
The visitors were quick to take advantage - scoring ten points in O'Connor's absence, including a second try as Basson touched down after being denied earlier. After the teams traded penalty goals (with Force pivot Willie Ripia taking over kicking duties), the Bulls reached the break with a 15-12 lead.
Points were hard to come by early in the second half, with Steyn's penalty in the 55th minute quickly cancelled out by O'Connor up the other end of the field (18-15).
O'Connor's hot kicking continued as he first leveled the scores with a pair of vital penalties, before Shepherd put the Force in front in the 68th minute when he grabbed a desperate pass from Ripia and touched down in the corner.
O'Connor's 77th minute penalty gave the Force an eight-point buffer, and although Steyn closed the gap back to five with two minutes remaining, the home side held firm in the dying stages.
Pens: O'Connor 6, Ripia
Tries: Ralepelle, Basson
Pens: Steyn 3
Western Force: 15 Cameron Shepherd, 14 Nick Cummins, 13 Patrick Dellit, 12 James O'Connor, 11 Rory Sidey, 10 Willie Ripia, 9 Brett Sheehan, 8 Ben McCalman, 7 Jono Jenkins, 6 Richard Brown, 5 Nathan Sharpe (c), 4 Sam Wykes, 3 Matt Dunning, 2 Ben Whittaker, 1 Pek Cowan.
Replacements: 16 Nathan Charles, 17 Kieran Longbottom , 18 Tom Hockings, 19 Tevita Metuisela, 20 Mark Swanepoel , 21 Mark Bartholomeusz, 22 Alfie Mafi.
Bulls: 15 Zane Kirchner, 14 Francois Hougaard, 13 Stephan Dippenaar, 12 Wynand Olivier, 11 Bjorn Basson, 10 MornÃ© Steyn, 9 Fourie du Preez, 8 Pierre Spies, 7 Dewald Potgieter, 6 Deon Stegmann, 5 Victor Matfield (c), 4 Bakkies Botha, 3 Werner Kruger, 2 Chiliboy Ralepelle, 1 Dean Greyling.
Replacements: 16 Gary Botha, 17 Rossouw de Klerk, 18 Danie Rossouw, 19 Derick KuÃ¼n, 20 Flip van der Merwe ,21 Francois Brummer, 22 Jaco van der Westhuyzen.
Referee: Mark Lawrence (South Africa)