Aaron Finch and Shane Watson star with the bat, while Mitchell Starc and Glenn Maxwell with the ball to seal victory
Having chosen to field, Australia's bowlers, led by Mitchell Starc and Glenn Maxwell, restricted South Africa to a modest 128 for 7, before the batsmen chased down the target comfortably with 30 balls to spare.
Chasing a double after having won the Test series 2-1, Australia had an ideal start with Finch and Cameron White, who came in for David Warner, starting things off. Finch began with two fours in the first over off JP Duminy and continued with his usual swashbuckling ways to add 43 runs off just 29 balls with White. Once Imran Tahir dismissed White for 14, Finch set up a 24-run second-wicket stand with Watson to take Australia to 67 for 1 in just eight overs.
With Australia running away with the game, Tahir returned to account for Finch for 39 and South Africa gained some hope thanks to some tight bowling by Wayne Parnell and Tahir that stemmed the flow of runs.
But this lasted only a couple of overs because Watson and Maxwell then smashed 18 runs off the 11th over bowled by Albie Morkel to take Australia 26 runs away from the target.
Although both batsmen fell in consecutive overs, Watson going after a 28-ball 35, it mattered little as George Bailey and Brad Hodge got the remaining runs with an unbeaten fifth-wicket stand worth 22 runs.
Earlier, Starc and Maxwell led a strong Australia bowling performance on a pitch, which had spent much of the previous two weeks under covers because of almost continuous rain.
Quinton de Kock was his team’s highest scorer with a 40-ball 41, which included two fours and two sixes, but none of his teammates were able to provide significant support. Morkel, however, provided some late fireworks with an 11-ball 18 that included two sixes.
Starc, who started with a rare maiden over for the format, took 2 for 16, while Maxwell claimed 2 for 19 to set up an easy chase for Australia.
The first game between the two sides, at Port Elizabeth last Sunday, was washed out, while Australia won the second game at Durban on Wednesday by five wickets.
South Africa and Australia now head to Bangladesh for the ICC World Twenty20 starting on Sunday.