The final day-nighter was eventually called off under the lights on Wednesday as rain ruined the finale, but Australia could still celebrate a satisfying 45-run (DLS method) victory on a day when they were vastly improved after their capitulation in chases in the first two matches.
Half-centuries from the rejuvenated Carey (74 off 88 balls) and captain Mitch Marsh, plus 48 from Ollie Peake, helped propel Australia to 9-322 after they'd been put in, with South Africa at no point then threatening to pull off the highest successful ODI chase ever at the ground.
And by the time the rain, which had also delayed the start by half-an-hour, returned to quite spoil the fun, Australia were already in full control.
Zampa (2-34 off six overs) rediscovered his best after recent struggles and Xavier Bartlett earned a couple of key early wickets (2-25 off five) as only Ryan Rickelton (71no off 81 balls) looked likely to trouble the visitors with South Africa limping to 4-145 off 28 overs.
Cummins may have returned as bowler only, not as the captain, with Marsh keeping the job for the third and final match, but his return seemed to enthuse everyone, with his 0-17 off five probing overs suggesting he'll be in fine shape to lead his troops in the first Test in Durban on October 9.
Stand-in Marsh again did his bit, leading from the front, as he powered to his third half-century of the series (56 off 42 balls) following his 60 and 84 in Durban and Johannesburg.
He and Travis Head (24 off 20) again provided an electric start with a 78 stand at nine-runs-an-over and this time the middle-order built much more assiduously against a Proteas' side who weren't helped by resting key spinner, player-of-the-series Keshav Maharaj, and captain Temba Bavuma among four changes.
It wasn't easy to start with, after Bjorn Fortuin trapped Marsh lbw and Gerald Coetzee bowled Cooper Connolly (23) with a brilliant yorker, but 20-year-old prospect Peake impressed again with Carey as they put on 73 off 88 balls, the sort of partnership Marsh had been crying out to see.
Peake, on 48, looked a bit crestfallen after he must have thought he'd cracked a boundary off Corbin Bosch to take him to his landmark 50 only for Fortuin to take a dazzling diving catch behind point to send him packing.
Matt Renshaw (30) and Carey continued the good work with a 66 stand but Australia didn't get the acceleration they'd hoped for in the dying overs, with Carey's 88-ball knock eventually ending at the hands of the excellent Bosch (4-60 off nine overs).
It was Carey's first international half-century in 17 ODI and Test innings since his Ashes hundred in Adelaide last December.
Cameron Green had an eventful time, taking a fearful beamer from Bosch straight into his box, but recovering to hit the next delivery, also a fast full-toss, courageously for six, only to then be bumped out next ball by a short one, seemingly suffering a muscle injury in the process.
It meant he wasn't fit to bowl, leaving an Australian attack already without the injured Nathan Ellis and Jack Edwards depleted, but after Bartlett struck to get rid of Quinton de Kock with a poor short ball, and skipper Aiden Markram with a terrific swinging full-ball, South Africa were soon on the back foot under the lights.
Zampa was back to his squeezing, probing best, luring the dangerous first-match centurion Matthew Breetzke to be stumped on 25 and trapping Tristan Stubbs lbw for 14.
