South Africa (23) 29
Try Matfield Pens: M Steyn 7 Drop-goal: M Steyn
Australia (10) 17
Tries Ashley-Cooper, Giteau Con: Giteau 2 Drop-goal: Barnes
Matfield benefitted from a surprising piece of skill from John Smit
South Africa put themselves in pole position to claim the Tri-Nations with victory over Australia in Cape Town.
Australia took an early lead through Adam Ashley-Cooper's try, but South Africa soon took control.
Morne Steyn's goalkicking and a try from Victor Matfield put the Boks 23-10 up at the break, with the Wallabies down to 13 men after two sin-binnings.
Matt Giteau's try gave the visitors hope but Steyn's kicks, and a third Wallaby sin-bin, sealed victory.
The victory maintains South Africa's 100% record in this season's Tri-Nations, while Australia are still searching for a first win of the campaign.
Australia got off to the perfect start, with George Smith acting as link man before a handling move was finished off by Ashley-Cooper in the corner inside the opening two minutes.
Giteau curled in the conversion from the touchline for a 7-0 lead, but it proved to be a false dawn for the visitors as South Africa took a stranglehold.
Australia's indiscipline gifted the in-form Morne Steyn three penalties in quick succession, and the fly-half continued where he left off against New Zealand last week with his unerring boot kicking the Springboks 9-7 ahead.
Berrick Barnes chipped over a drop-goal on a rare Australia foray into South Africa territory, but South Africa - aided by the ability to steal Wallaby line-out ball almost at will - soon regained the lead with another Steyn penalty.
Steyn's drop-goal, after a turnover courtesy of the outstanding Heinrich Brussow, extended South Africa's lead before the wheels began to come off for Australia.
A steepling up-and-under was fielded by Ashley-Cooper, but some ferocious work at the ruck saw South Africa come away with possession.
The ball found its way to John Smit, and the burly prop produced a lovely grubber kick which resulted in Matfield busting over from close range.
Influential Wallaby skipper Stirling Mortlock was forced off through injury and soon after Giteau received a deserved yellow card for a cynical challenge - leading with his elbow - on Fourie du Preez as he chased an up-and-under.
It got worse for the Australians as an embarrassingly obvious attempt by flanker Richard Brown to steal the ball from the wrong side saw the Wallabies reduced to 13 men.
Smith's yellow card late on was Australia's third of the match
Steyn punished them with another penalty, but the seriously stretched Australia defence just about kept South Africa out despite a wave of attacks on the cusp of half-time.
Australia came out for the second half with the clear intention of playing for territory until they were back to 15 men, and the boot of Berrick Barnes ensured they were successful in their aim.
Steyn's sixth penalty extended South Africa's advantage, but Australia were gradually playing themselves back into the game.
With their scrum very much on top, Australia showed what they could do in attack as impressive replacement James O'Connor raced down the touchline before kicking ahead.
Nathan Sharpe was held up over the line, but from the resulting try Giteau showed delightful footwork to beat two men and score next to the posts.
South Africa responded well, squeezing Australia at the breakdown before Smith's yellow card with four minutes left - punished by another kick by the prolific Steyn - effectively ended Australia's hopes.
Springboks coach Peter de Villiers struggled to disguise his pleasure after his side's third straight Tri-Nations win.
"As a coach you can never be satisfied, and you'll always go for better," said De Villiers.
When you score two tries to one, you don't normally lose, but we gave away too many penalties
Australia coach Robbie Deans
"But it's working well at the moment, it's brilliant. The players read the situations very well. We are kind of where we want to be."
But Australia coach Robbie Deans admitted his side's indiscipline had been a major factor in their defeat, despite their brave display either side of half-time with two men in the sin-bin.
"The yellow cards made life a lot harder but it was a pretty good effort with 13 men. Our defence was good under the circumstances but our energy was sapped," he said.
"The cards didn't help our prospects in the game, though. I'm not sure of the number of penalties we gave away but I think eight out of 13 were shots at goal, seven were converted and that makes life very difficult.
"When you score two tries to one, you don't normally lose, but we gave away too many penalties."
South Africa: F Steyn; JP Pietersen, J Fourie, J de Villiers, B Habana; M Steyn, F du Preez; T Mtawarira, B du Plessis, J Smit (capt), B Botha, V Matfield, H Brussow, J Smith, P Spies.
Replacements: C Ralepelle, J du Plessis, A Bekker, D Rossouw, R Januarie, R Pienaar, A Jacobs.
Australia: A Ashley-Cooper; L Turner, S Mortlock (capt), B Barnes, D Mitchell; M Giteau, L Burgess; B Robinson, S Moore, A Baxter, J Horwill, N Sharpe, R Brown, G Smith, W Palu.
Replacements: T Polota-Nau, B Alexander, D Mumm, D Pocock, W Genia, P Hynes, J O'Connor.