After being sent in, du Plessis (125) and Miller (139) put on a 252-run stand - the biggest ODI partnership against Australia.
Steyn was the pick of the bowlers for South Africa, returning 3/45 from 10 overs, while Pretorius got 2/61.
But Du Plessis eventually indicated for the review though he was reminded that technically Miller had to provide the signal.
There were significant phases of the innings, with century-maker Shaun Marsh to the fore, when Australia seemed right in the contest on a trustworthy surface that promoted some especially crisp, savage driving and pulling.
"After 35 overs we were in a great position but they took it away at the end".
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The visitors were asked to bat first by the hosts. But Steyn took out Carey on the last ball of his ninth over, finding an edge to Quinton de Kock.
However, Pretorius swung the game back in South Africa's favour by dismissing Marsh in the next over, when the left-hander looked to whip one towards the leg side but ended up skying it to Heinrich Klaasen at wide long-on.
Miller and du Plessis chose to review after a lengthy deliberation that appeared to take longer than the allowed 15-second window.
Miller was the more aggressive of the two, smashing 13 fours and four sixes in his 108-ball knock while du Plessis went at his own pace, hitting 15 fours and four sixes during his 114-ball stay.
Miller made the landmark in 95 balls, including eight fours and two sixes, and was finally caught at deep midwicket off Josh Hazlewood in the last over.
Australia's woes were compounded when Aaron Finch soon followed him back to the pavillon.