The Bulls' Super Rugby title defence is hanging by a thread after suffering a 26-21 defeat to the Western Force in Perth on Saturday night.

Force fullback Cameron Shepherd scored the match-winning try 12 minutes from time and also pulled off a desperate, try-saving tackle earlier in the half to propel the Force to their third victory of the season and second on the trot.

The Bulls, winners of the past two titles, face an almighty task to even qualify for this year's finals, with their third straight loss leaving them with just four wins from nine games.

Force whiz kid James O'Connor nailed six of seven kicks for an 18-point haul, the speedy 20-year-old also creating numerous opportunities in open play.

The Force couldn't break through the Bulls' resolute defence in the opening half, with three penalties to O'Connor and another to Willie Ripia the only reward.

The Bulls looked dangerous every time they entered their attacking 22m, with hooker Chilliboy Ralepelle barging over in the 11th minute and winger Bjorn Basson adding the visitors' second just eight minutes later.

Basson's try arrived just a minute after O'Connor was harshly sin binned for a lifting tackle on Bulls fullback Zane Kirchner, who twisted in the tackle and landed heavily on his back.

The Bulls added 10 points to three during O'Connor's spell on the sideline, but a determined Force closed the deficit to just 15-12 by half-time, capitalising on several glaring handling errors by the visitors.

Force scrumhalf Brett Sheehan was a fired up customer and understandably so after copping an off-the-ball elbow to the head from Bulls prop Dean Greyling late in the first half.

Points were hard to come by early in the second half, with Morne Steyn's 55th-minute penalty quickly cancelled out by O'Connor up the other end.

Shepherd's first heroic act came in the 51st minute when his desperate tackle pushed Jaco Pretorius' boot into touch just as the Bulls centre dived forward in an attempt to score a try.

O'Connor's hot kicking continued as he nailed a pair of vital penalties, and 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.

"Those two moments were very important in the context of the win," Force coach Richard Graham said of Shepherd's try and desperate tackle.

"I thought the forwards in particular around the fringes ... were really physical in defence and we took them to ground really quickly.

"(Winning tonight) was very important for us on the back of winning last week. I thought the team was absolutely outstanding."

Bulls coach Frans Ludeke said his men made far too many handling errors.

"I thought that last 20 minutes we lost momentum and made a few mistakes," Ludeke said.

"We controlled possession in the first half and converted points but in that last 20 it slipped away."

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