The Bulls slowed the NSW Waratahs' charge to the Super 14 finals on Saturday night with a dour 20-6 victory at the Sydney Football Stadium.

Tries to winger Bryan Habana and prop Werner Kruger and two conversions, a penalty and drop goal from five-eighth Morne Steyn were enough to end the Waratahs' record-setting 11-match winning streak at the SFS.

The defeat relegated NSW to fourth spot on the ladder after nine rounds and put the Tahs' playoff hopes on a knife's edge.

With a derby against the Western Force in Sydney next Saturday night before a bye and a testing three-game stretch in South Africa to complete their home-and-away campaign, suddenly the Waratahs are under real pressure to qualify for the finals.

Boasting the biggest and meanest forwards in the tournament - not to mention three straight triumphs over NSW - the Bulls were always going to be a tough nut to crack.

Typically, the match was a dour one - with controversial South African referee Jonathon Kaplan not improving the contest as a spectacle with his pedantic controlling of play.

He called countless plays back for so-called forward passes - which replays suggested were not - and was heard to make one of the quotes of the year when asked by Waratahs prop Dan Palmer why he had awarded two straight scrum penalties in the second half.

"I can't remember," said Kaplan, who was roundly jeered by the exasperated crowd at fulltime.

The Bulls had led 7-3 at halftime following Habana's try in the 16th minute, after the visitors intercepted an errant lineout throw from NSW hooker Tatafu Polota-Nau inside the Waratahs quarter.

The Waratahs' only points before the break came from a penalty goal to five-eighth Daniel Halangahu after the halftime siren.

Steyn extended the Bulls' advantage to 10 points with his drop goal and penalty early in the second stanza before replacement flyhalf Kurtley Beale added a penalty - the last points of the night for the Waratahs, who again struggled with their attacking execution.

Kruger's try 12 minutes from time sealed the Waratahs' fate.

NSW captain Phil Waugh said he sensed the Waratahs may have entered the pivotal encounter mentally drained.

"It's probably a product of being in the ninth round and having a lot of close games," he said.

"It's not a lack of effort, but there was certainly a lack of spark.

"Perhaps because we're not making the most of our opportunities early in the game, guys subconciously were a little bit off mentally.

"I don't think it's an issue that will repeat itself. There was a huge amount of effort from the guys.

"But at this level, it's such a fine line between winning and losing games. It's just that energy level that's the difference and it's probably fair to say that they had that edge on us.

"It felt like we never really got any momentum, no rhythm, after that first 10, 15 minutes."

Ultimately, though, Waugh said the Waratahs paid the price for 30 turnovers going the Bulls' way.

"If you turn over that much ball, it doesn't matter who you're playing; you're going to lose the game," he said.

"We played most of the game in our own half and they put a lot of pressure on us at the set piece, which made it hard to get out of our own half."

The Waratahs' woes were compounded by a hamstring injury to Rob Horne which is likely to sideline the young centre for two weeks, while Lachie Turner suffered a suspected broken nose.

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