Shane Watson collected yet another man-of-the-match award as he inspired his side with two for 29 from his four overs and 70 from 47 balls.
Australia lost just two wickets as they strolled to their victory target of 147 to claim their fourth successive victory in Sri Lanka, while the Proteas slumped to their second defeat of the Super Eights.
South African were lacklustre with the bat and sloppy in the field, and while the result has not yet knocked them out of the tournament, they will now need other results to fall their way if they are to progress to the semi-finals.
After being asked to bat first, South Africa made an extremely sluggish start as Richard Levi departed for a three-ball duck as spinner Xavier Doherty, playing his first match of the tournament, made the early breakthrough.
Hashim Amla briefly looked assured at the crease with a quick 17, but his stay at the crease was ended by the inspired Watson, with wicketkeeper Matthew Wade taking the catch behind.
Jacques Kallis was moved up to number three, but he did not trouble the scorers as he was snaffled behind by Wade for just six off the bowling of the excellent Doherty.
JP Duminy and captain AB de Villiers gave their side real impetus in the middle order, with the number four scoring 30 off 36 balls before Doherty claimed his third wicket courtesy of a comprehensive stumping.
Watson accounted for de Villiers with the captain well set at the crease on 21, but the Proteas still managed a late assault to build on a very mediocre score.
South Africa plundered 54 runs from the final four overs of their innings to post a competitive, if un-intimidating, total of 146 for five with Farhaan Behardien and Robin Peterson weighing in with 31 and 32 not out, respectively.
Australia did not manage to get off to the best of starts themselves, as the ever-dangerous David Warner fell for just five, attempting to slog a full delivery from Morne Morkel which scattered his woodwork.
But Watson was brimming with confidence and bludgeoned eight fours and two sixes as he led the charge with Australia able to coast towards their total.
Mike Hussey, batting at number three, scored an unbeaten 45 off 37 balls as he joined forces with Watson and the pair ensured that South Africa were not able to make further inroads.
Watson, who boasts scores of 47, 51, 41 not out, 72 and now 70 from his last five T20 internationals, eventually holed out to Wayne Parnell at long on as Peterson took his wicket with six overs remaining.
It was left to Cameron White, who plundered a quick 21, and Hussey to steer Australia to their target with 14 balls remaining as South Africa were left to confront a second defeat in the Super Eights.
For Australia, it was another comprehensive victory as they close in on the semi-finals, while de Villiers was left to bemoan his side’s lack of a cutting edge as they look all but out of the competition at the last-eight stage.