A great performance in the first-half set up a 32-18 victory for South Africa in the semi-final of the U19 World Championship.
The Baby Boks will play New Zealand in the final after the Kiwis beat Wales 36-12.
The South Africans forwards were dominant at the breakdown, setting up a great attacking platform for their dangerous runners and making some crucial turnovers on defence. The young Australians had few answers when the Baby Boks countered, as the boys in green and gold kept the ball alive superbly.
South Africa enjoyed plenty of possession early on, but failed to capitalise on all of their opportunities. Hooker Henri Bantjies scored in reply to an early Aussie penalty, and the Boks should have had a couple of more in subsequent movements.
Fullback Wilton Pietersen eventually finished after some smart stepping in the Aussie 22, and a Stefan Watermeyer penalty ensured they went to the break 15-3 up.
Second-rower Cornell Hess was rewarded at the beginning of the second period as the South African forwards began to take the opposition apart.
But the Aussies never gave up and a great drive from a line-out saw them trailing by 20-8. South Africa answered with a spectacular 80m try that was eventually dotted dow by flyhalf Francois Brummer, but some slack defending saw the Aussies pick up a soft score from a quick throw-in.
Another was smartly finished by Aussie winger Alfi Mafi who got his side a touch closer to an improbable comeback.
However, Eric Sauls’s charges had the final say, a kick into space bouncing favourably for Stephan Dippenaar, who picked up a deserved five points for a fine performance in the midfield.
The resounding win sees the Baby Boks advance to the final against New Zealand on 21 April.
South Africa – Tries: Henri Bantjies, Wilton Pietersen, Cornell Hess, Francois Brummer, Stephan Dippenaar. Conversions: Stefan Watermeyer (2). Penalty: Watermeyer.
Australia – Tries: Michael Uoka, Rob Simmons, Alfi Mafi. Penalty: Rowan Kellam.