They won the fifth one-day international by 31 runs to become the first team to inflict a 5-0 hiding on Australia.
SA scored 327/8 and dismissed Australia for 296 in 48.2 overs.
Despite a defiant century by David Warner the Australians were rarely in the running for a target that was 70 runs bigger than any successfully chased in the 38 ODIs played here.
The home side’s tower of runs was built on the performance of Rilee Rossouw, who added his name to the honour role of South Africans who have scored hundred in the series.
Rossouw hammered 122 to join Quinton de Kock, Faf du Plessis and David Miller among SA’s centurions.
A replacement for the injured AB de Villiers, Rossouw scored half-centuries in the first two matches and came to the crease on Wednesday after De Kock and Hashim Amla had been dismissed with 37 on the board.
Four overs later SA were 52/3 when Joe Mennie nailed the top of Du Plessis’ stumps.
But the Australians were denied further inroads as Rossouw and JP Duminy righted the innings with a stand of 178 that endured into the 39th over.
It was ended when Duminy, who scored 73, shaped to drive and slapped a catch to backward point.
Rossouw went next, caught at long-on off the 118th ball he faced in an innings brimming with emphatic, meaty strokes that soared and streaked to all parts of the ground on the wings of confidence.
His dismissal put paid to a partnership of 51 shared with Miller, who made a surprise return to action after being ruled out for the rest of the series with a groin injury after the third match at Kingsmead last Wednesday.
Mennie went wicketless on debut at the Wanderers on October 2. But on Wednesday, in his only other game in the series, he had 2/5 after three of his overs and finished with 3-49.
The Aussies were left clutching at such straws of positivity in another underwhelming display with bat and ball.
Another came from Warner, who should have been caught behind for 11 in the sixth over, when Kagiso Rabada found the edge. Instead, De Kock dived and dropped the catch.
Warner survived to make 173, the highest score by an Australian in ODIs against SA.
He showing the experience of his 85 ODIs by not missing an opportunity to gather runs even though he batted within himself throughout.
While Warner and Finch were together in their opening stand of 72 Australia looked like they might make a fist of things.
It took Imran Tahir to change that script in the space of three balls by bowling Finch with a straight delivery that hurried on - a flipper, perchance? - and then clattering a googly into Steve Smith’s stumps.
Their momentum snapped, even the famously pugnacious Aussies looked like they were packing for Perth.
Warner ensured they were not embarrassed and there were worthy efforts from Mitchell Marsh and Travis Head and a series of fiery exchanges between Warner and Tahir.
Tahir’s brilliant throw from deep point to run Warner out in the 48th over was thus poetically correct.
Even Warner’s wonderful innings was not enough to stave off what had been unthinkable when the series started.
You are not dreaming. This is not a joke. It will not be overturned. Yes, 5-0. Yes, really.