With this four wicket win, hosts (South Africa) have also clinched the 5-match series with two more games to spare. Kangaroos are still searching for an ODI win in the ongoing series.
Chasing a challenging total of 372, Miller and Quinton de Kock (70) were the chief architects of Proteas' second highest run chase against same opponents.
This is the second highest successgul run chase in the history of the game, highest being South Africa's record chase of 434 against Australia in 2006.
The Proteas were struggling at 265/6 in 37.4 overs when Miller, who went on slamming his 3rd ODI ton, got the support of Andile Phehlukwayo put up a match-winning unbeaten 107 run partnership off 70 balls for the seventh wicket.
Phehlukwayo remained unbeaten at 42 and also hit the winning runs for the side in the final over with four balls to spare.
Miller's 118 run innings comprised 10 boundaries and 6 massive sixes. What makes this innings more special is the fact that Miller pulled his groin muscle during the match, but continued playing.
Earlier, David Warner and Steve Smith slammed centuries to lead a strong Australian batting performance in the must win game.
The left-handed Warner hit 117 and skipper Smith made 108 as Australia made 371 for six, a ground record, after winning the toss and electing to bat. It was only the third time in 42 one-day internationals that a team had made 300 or more at Kingsmead, a ground which seldom yields big totals.
Warner and Aaron Finch gave Australia a blazing start, putting on 110 for the first wicket off 81 balls, with fast bowler Dale Steyn leaking 96 runs from his quota of 10 overs. Although Steyn picked up two wickets but this was his most expensive one-day outing.
But introduction of leg-spinner Imran Tahir decelarated Australia's run speed. The change of pace worked in South Africa's favour but the Aussie's exploits in the death overs (71 runs in last five overs) ensured the visitors post a daunting total.