The Stormers have dealt the Brumbies' Super 14 playoff hopes a potentially fatal blow with a 20-10 victory in Cape Town.

The loss left the Brumbies in eighth spot, seven points behind the fourth-placed Stormers, with just two rounds remaining.

Hit by a controversial first-half penalty try award by New Zealand referee Steve Walsh, who also sin-binned Brumbies five-eighth Christian Lealiifano at the same time, the visitors trailed 20-0 after just 27 minutes.

The shellshocked Brumbies regrouped after the break and capitalised on more possession and improved ball control to outscore the home team 10-0 in the second half, with winger Adam Ashley-Cooper and replacement lock Peter Kimlin scoring tries.

But it was not enough to deny the Stormers their seventh win in their last eight games.

The South Africans are now in fourth spot, just two points behind the second-place NSW Waratahs, who they host next weekend in what looms as another pivotal encounter at Newlands.

The Stormers' victory was only their second in 11 games against the Brumbies and their first in 10 years.

It also ended a three-game winning streak which had reignited the Brumbies' campaign.

The visitors couldn't generate much forward momentum in the first half, during which they found it hard to contain the Stormers centre pairing of skipper Jean de Villiers and Gcobani Bobo.

An 11th-minute break by Bobo set up Springboks stalwart de Villiers for the opening try.

Five-eighth Peter Grant converted and kicked a 20th-minute penalty to blow the lead out to 10-0.

Moments later, de Villiers claimed Mark Gerrard's restart following Grant's penalty and raced down the left hand side of the field.

As he was tackled by fullback Gerrard, de Villiers threw the ball infield and Walsh awarded a penalty try when Bobo was deemed to have been tackled prematurely by Lealiifano, who received a yellow card.

It seemed a harsh ruling as it did not appear a particularly strong challenge on Bobo was not even grounded by the tackle.

"Off that kick-off that try pretty much broke our backs," Brumbies skipper and centre Stirling Mortlock said.

"But full credit to our guys, we came back in the second half, but the Stormers were too good tonight."

Grant again converted and added another penalty to give the rampant Stormers a 20-0 halftime advantage.

The Brumbies came close to scoring a couple of times in the last two minutes of the half and carried their resurgence into the second stanza.

Centre Tyrone Smith slashed through the Stormers defence to set up Ashley-Cooper's try in the 54th minute.

The try went unconverted, but the Brumbies continued to threaten, with Ashley-Cooper proving especially dangerous and hard to bring down.

The Stormers pressed hard for another try in the closing stages, but the Brumbies defence held firm and Kimlin crashed over the line in the final minute.

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