This means that South Africa will face England in the first semi-final in Bristol on Tuesday, July 18.
Australia were restricted to a competitive 269, bowled out for the first time in the tournament so far after winning the toss and electing to bat first.
Nicole Bolton (79) and Beth Mooney got the innings off to a strong start, sharing a 114-run opening stand before Ayabonga Khaka struck in the 22nd over, clean bowling the latter for 53.
Captain Dane van Niekerk capitalised on the fallen wicket in the next over, removing her stand-in counterpart, Rachael Haynes without scoring, making her the South African skipper's 14th victim in the competition so far.
The Proteas did not have to wait long for another wicket to fall. Sune Luus, who returned her second ODI five-wicket haul, picked up her first when she stopped Bolton in her tracks in the 28th, ending what was a good knock until then.
The experienced Ellyse Perry absorbed the pressure however, striking a 58-ball 55 before she became Luus' next victim. The 21-year old struck again a ball later, bowling Elyse Villani out for a first-ball duck.
The Southern Stars were 154/4 in the 29th over when Alex Blackwell and Alyssa Healy put on 75 quick runs for the fifth wicket. Van Niekerk was the partnership breaker, getting the former out when she chipped the ball to Masabata Klaas at mid-on for 33 (40 balls, 4 fours). Healy only lasted one more over, but she made it count, striking three boundaries in a row before pulling the ball to Moseline Daniels at long-off and departing for 16 from 10.
Luus' last wicket was Ashleigh Gardner (4), who was also caught by Daniels. She ended with 5/67 in her 10 overs before Kapp mopped up the remaining wickets of Megan Schutt and Kristen Beams for 11 and none respectively. Australia were bowled out with nine balls to spare.
South Africa's reply did not get off to an ideal start when they lost Lizelle Lee to Jess Jonassen for nine after she tried to go big, but was caught by Haynes at mid-on instead. Laura Wolvaardt was once again impressive, hitting 71 from 94 balls (7 fours). She shared a 67-run, second-wicket stand with Trisha Chetty that steered the side back on track before hesitation between them resulted in the run out of the latter for 37.
Australia's Haynes, Jonassen and Perry returned two wickets each to help restrict the South Africans to 210.
Mignon du Preez (20) and Marizanne Kapp (19) managed to get starts, but were unable to kick on. Luus and Van Niekerk soon followed for six and one respectively. Ayabonga Khaka and Masabata Klaas were also dismissed for none and nine respectively as Shabnim Ismail made the last stand, hitting 26 from 41 deliveries. Hers was the last wicket to fall off the last delivery of the match.