After being put in to bat the toss, Laura Wolvaardt's charges slumped to 97 all out in 24 overs with Australia spinner Alana King taking 7-18, the best in the history of Women's World Cups.
Australia lost two early wickets in the run-chase but the target was never enough and they eventually reached the total in the 17th over.
The Proteas Women got off to a decent start with the bat as they reached 32 in the seventh over with Wolvaardt dominating while hitting seven boundaries.
The wheels came off though when the South Africa skipper was the first wicket fall for 31, seamer Megan Schutt making the breakthrough.
Fellow seamer Kim Garth then trapped Tazmin Brits lbw for just 6 with the total on 46-2 in the 10th over.
King was then introduced to the attack and immediately made inroads as the Proteas could not cope with the leg-spinner as she ran through batting order.
Sinalo Jafta scored a fighting 29 in amongst the carnage but King was superior and broke all sorts of records in her spell.
Chasing a low total, Phoebe Litchfield was caught at slip off seamer Marizanne Kapp while Masabata Klaas got rid of Ellyse Perry to leave Australia 11-2.
Georgia Voll (38 not out) and Beth Mooney (42) then combined to settle any nerves as Australia continue their unbeaten run in the global tournament.
The Proteas Women will take on England in the semifinals while Australia play co-hosts India.
Fatima Sana and Chamari Athapaththu both looked to the future after a frustrating day in Colombo saw Pakistan and Sri Lanka end their ICC Women's World Cup campaigns with a washout.
Australia batter Travis Head is hoping seamer-friendly pitches in the Ashes because he says it will help his stroke play.
Australia defeated India by two wickets in the second ODI of the series at the Adelaide Oval after a nervy finish that very nearly saw the visitors pull off an unlikely victory.
Ashleigh Gardner's blistering century and Annabel Sutherland's unbeaten 98 powered Australia to a stunning six-wicket victory against England at the ICC Women's World Cup.
