Captain fantastic Meg Lanning has guided Australia to a sixth-straight World Cup win, making an unbeaten 135 in a successful chase of South Africa's 5-271.
Australia were under pressure at Wellington's Basin Reserve after the Proteas put together a fine total, fired by Laura Wolvaardt's 90.
After weathering a fantastic early spell by Shabnim Ismail, Australia knuckled down, reaching 5-272 with 28 balls remaining.
Fresh from a match-winning 97 against India on Saturday, Lanning was central again on Tuesday.
The Victorian played a composed hand before taking flight, striking 15 fours, one six and finding runs in all corners of the ground to become the tournament's highest runscorer with the monster knock.
The Australian skipper stepped up in the absence of top-order bat Ellyse Perry, who hurt her back bowling, to score her 15th ODI century.
"It was nice to contribute," Lanning said with typical modesty.
"We speak a lot about the top four trying to bat through and playing those match-winning innings. It was me today, it will be someone else another day (but) it was nice to be there at the end."
South Africa's sliding doors moment arrived early in Australia's chase when Ismail was desperately unlucky not to snare the Aussie skipper during a ferocious start.
Ismail, the World Cup's leading wicket taker, had Alyssa Healy caught behind for one and was on the warpath, twice drawing edges from Lanning that were put down or missed behind the wicket.
She had lost none of her intensity on her return to the attack, taking the wicket of Tahlia McGrath and sending death stares to Lizette Lee for missing catches at slip and gully.
"She was bowling quick," Lanning said.
"I thought (Marizanne) Kapp and Ismail bowled extremely well. I probably left more balls than I ever have."
Rachael Haynes (17), Beth Mooney (21), McGrath (32) and Ash Gardner (22) all played supporting acts to the Lanning show, with Annabel Sutherland (22 not out) alongside her captain to hit the winning runs.
Lanning won the toss and opted to field but without rested pace bowler Darcie Brown, Australia struggled to make an early breakthrough.
Wolvaardt and Lee were unconcerned to be sent in, becoming the first opening pair to survive a powerplay against Australia with an 88-run stand.
Late hitting from Sune Luus (52 off 51), Marizanne Kapp (30 off 21) and Chloe Tryon (17 off 9) ensured the Proteas' biggest total of the tournament.
No Australian bowler took more than a sole wicket, though Gardner produced fireworks with a one-handed screamer on the boundary to stop a six and dismiss power hitter Mignon du Preez.
The win means Australia will finish top of the group stage - barring a capitulation against Bangladesh on Friday - and gives the world No.1s a fresh world record.
After 18 straight successful chases, Lanning's side have overtaken the Indian men's side of 2005-06 for the most consecutive ODI wins batting second.
The result is South Africa's first loss of the tournament, though they are still highly likely to make the semi-finals.
