Chasing 232 for victory, the Proteas rode on David Miller's half-century and captain Faf du Plessis' patient knock to come close to the target but eventually fell short and were restricted to 224 for 9 in 50 overs.
They put the chase on pace with a game-high 74-run partnership before du Plessis (47 from 65 balls) hit his stumps from Cummins' bowling.
However, from a pure cricketing perspective, the Proteas and Aussies are actually in the exact same situation - eerily so after Aaron Finch and his troops squared the ODI series at one-all with a seven-run win in Adelaide on Friday.
Australia lost 5/71 thereafter as South Africa smashed through the middle- and lower-order, but as in Perth last Sunday, they allowed the last-wicket pair to give the hosts a lift, giving them a respectable total, but not one that should've been a winning one.
Australia have named a 13-member squad for the upcoming Twenty20 Internationals against South Africa and India without the experienced trio of Mitchell Starc, Mitchell Marsh and Nathan Lyon.
"While I know all four (Starc, Siddle, Lyon, and Marsh) have a desire to be playing cricket for Australia in every format, with a really tough Test series against India coming up, we believe their best preparation is to go back and get some really good cricket under their belts in the Sheffield Shield", Australia head coach Justin Langer said.
The South Africans slipped to 68 for 4 inside 15 overs before Miller and du Plessis fought back. "We needed our quicks to come through".
It makes for a pleasant selection dilemma for Sunday's series decider in Hobart.
Earlier, the Proteas produced yet another impressive performance with the ball as they bowled Australia out for 231 after electing to bowl first.
The Australians were all out in 48.3 overs - the seventh time in their past eight one-day internationals they have failed to bat out their allotted overs. Alex Carey top-scored with 47 from 72 balls for Australia, Chris Lynn added 44 from 44 deliveries, and captain Aaron Finch 41 from 63 balls.
Dale Steyn (2/31) and the hostile Kagiso Rabada (4/54) combined superbly once again, while the seamers of Dwaine Pretorius proved surprisingly effective as he grabbed 3/32.
Cross-seamed deliveries and cutters brought the most profit for bowlers on both sides, Dwaine Pretorius picking up 3 for 32 in the afternoon and Marcus Stoinis making several crucial breakthroughs for a return of 3 for 35 that turned the match decisively. Miller (51), Stoinis (3/35), Hazlewood (2/42).