As a reconnaissance mission for their World Cup defence in southern Africa in a year's time, Sunday's loss felt like another alarming capitulation after a fine start to their pursuit of a big Proteas total was wasted, just as on Thursday in the first-match collapse at Durban.
Chasing South Africa's formidable 9-365, which featured superb hundreds from captain Temba Bavuma and the ever-reliable David Miller, Australia's stand-in skipper Mitch Marsh and Travis Head, who'd teed off with a brisk 90 together in Durban, this time clattered 130 off 17 overs at the Wanderers.
But the same old failings of cheap dismissals and an inability to build partnerships came back to haunt the visitors, with not even a rousing late show of defiance from Xavier Bartlett, with a thumping 50 off 28 balls, able to get them to within a sniff of the target as they succumbed to 333 all out with one ball remaining.
After losing a second straight match in which they'd won the toss and inserted the Proteas, Australia, who again kept captain Pat Cummins on ice with the Test series around the corner, were left with further big concerns over their middle-order stuttering in the face of quality spin.
"Really disappointing - we came here to ensure the series went to the last game but, fair play to South Africa, ultimately we've been outplayed again," sighed Marsh.
"In both games, the way we've set up the innings has been really good, but we just haven't been able to execute in those middle phases."
With a third match to come in Potchefstroom on Wednesday, Marsh shrugged: "We've got to keep improving, we don't want to be whitewashed."
Cummins was unquestionably missed and a side injury that ensured their outstanding quick Nathan Ellis could bowl only four overs on Sunday meant their attack was always under pressure, even if Jack Edwards offered genuine all-round promise with 5-67 and a solid knock of 25 in support of Bartlett.
"It was massive to lose Nathan for the death overs, and we had to figure it out from there," Edwards said.
Josh Hazlewood took three wickets while going at seven an over, but more alarming was Adam Zampa's continuing struggles, as he went for 0-77, in stark contrast to South Africa's testing spin trio of Keshav Maharaj (2-54), Bjorn Fortuin (2-70) and Aiden Markram (1-55).
They helped really put the brakes on Australia's chase after Marsh and Head had cracked 84 apiece, the captain's knock featuring five sixes and 10 fours off 53 balls and Head's start coming off 103 balls, with one six and 12 fours.
Apart from the openers, though, Australia were soon struggling, Cooper Connolly chipping one tamely off Lizaad Williams (3-54) to short mid-wicket to depart for 10, and wicketkeeper Alex Carey trapped lbw for 17 by Maharaj, who then did the same to dismiss Matt Renshaw for 32.
Cameron Green had a struggle, limping to 17 off 34 balls, before Bartlett showed him the way belatedly with five mighty sixes, only for his innings, and Australia's last hope, to be ended by a cracking leg-before yorker from Williams.
Earlier, South Africa had the Bullring buzzing as man-of-the-match Miller smashed nine sixes on his way to 142 off 93 balls, while Bavuma hit 103 off 116, the pair sharing in a superb fourth-wicket stand of 156.
Edwards went wicketless in his ODI debut on Thursday, but proved the pick of the bowlers, getting rid of both centurions and leaving Marsh to concede there was reason to feel the future was bright.
