He somehow contrived to miss the conversion of Victor Matfield's first-half try, but that didn't matter. The Boks took full advantage of their physical superiority up front and benefited from facing an Aussie side that conceded three yellow cards.
The visitors' drew first blood with a first minute try from full back Adam Ashley-Cooper, but once Heinrick Brussow got the measure of the Wallabies at the breakdown the penalties flowed the home side's way and Steyn did the rest.
The Bull's outside half has made an incredible contribution to the world champions' cause aking his debut as a second half replacement against the British & Irish Lions in the first Test in Durban.
Having topped the Super 14 point scoring charts after guiding the Bulls to victory in that tournament, he has notched 83 points in six outings at the start of his Test career and is averaging 21 points per game in this season's Tri-Nations campaign.
This is the story of his fairy tale start on the international stage:
1st Test v Lions: Try saving tackle on Ugo Monye when he knocked the ball out of the winger's hands as he crossed the line.
2nd Test v Lions: Played final 10 minutes and scored 10 vital points. Converted two tries and then landed the 54 metre penalty to win the game, and the series, with the final kick of the match.
3rd Test v Lions: First start and first defeat. Scored all nine points for his team in 28-9 defeat.
Tri-Nations v NZ 1: Kicked three penalties after coming on as a replacement for Ruan Pienaar.
Tri-Nations v NZ 2: Scored a Tri-Nations record 31 points as he accounted for all his side's points in their 31-19 win in his first Tri-Nations start.
Tri-Nations v Aus 1: Knocked over 24 points with the boot as the Boks continued their winning ways.
Once again the Boks were beaten on try count - Matt Giteau scored a consolation second try for the Aussies after the break - but the pressure and intensity generated by the home forwards was such that Stirling Mortlock's visitors had no real reply.
Matfield's sixth Test try, scored on the day he celebrated his 50th international in tandem with Bakkies Botha in the Boks' boilerhouse, came from an outrageous piece of skill from skipper John Smit.
Receiving the ball in the outside half slot from a ruck he heard Bryan Habana call for the kick ahead to the left and responded with an inch perfect left footed grubber that forced Lachie Turner to panic, loose the ball on his line and allow the giant Matfield to stoop and conquer.
The Aussies picked up two yellow cards before the break - Giteau for an outrageous airborne challenge on Fourie du Preez and Richard Brown for a ruck infringement - and another Steyn penalty meant the Newlands crowd were able to sit comfortably in their seats at the interval with their side 23-10 to the good.
The Wallabies, who had had to wait three weeks for their second game in the tournament after losing to the All Blacks in Auckland in their first outing, improved in the second half and rising star James O'Connor paved the way for Giteau to score their second try.
But penalties six and seven from the Steyn boot meant there was no cause for concern for the world champs, who now look like adding the 2009 Tri-Nations title to their bulging trophy cabinet.
Scorers: South Africa: Try: V Matfield; Pens: M Steyn 7; DG: M Steyn
Australia: Tries: A Ashley-Cooper, M Giteau; Cons: M Giteau 2; DG: B Barnes
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