The Aussies won the toss and elected to bat but openers Ines McKeon and Grace Lyons were removed early on by Nthabiseng Nini without making any real contributions.
Captain Lucy Hamilton and Caoimhe Bray put up a decent middle order partnership but Protea spinner Ashleigh van Wyk had other ideas for their innings.
Van Wyk began a destructive spell of 4/17 from 3 overs which won her the player of the match award. Seshnie Naidu and Kayla Reyneke picked up a wicket each.
Van Wyk said she kept herself calm through each ball and stuck to what worked for her.
“You always need support to achieve victory. It’s never just about what I do, t’s about the way my teammates and management back me. That support allows me to play with heart and without regrets, whether things go my way or not.
“As a team, we rely on our management for mental preparation, but the key to lifting the trophy is playing for each other. We back each other, celebrate each other’s successes as if they were our own, and function as a family and a unit,” she concluded.
With mounting pressure from the Proteas fielding attack during the tail end, Australia finished their 20 overs on 105/8.
Jemma Botha once again delivered for her side and got them off to a good start, knocking 37 from 24 before she was removed from the crease by Lucy Hamilton.
Simone Lourens and Faw Cowlings lost their wickets for scraps before Captain Reyneke arrived at the crease. She scored 26 from 26 before Hamilton again got the big wicket for Australia.
Wicketkeeper Karabo Meeso contributed a nifty 19 from 29 to help push the Proteas over the final stretch, winning the game in 18 overs.
Reyneke said her side would have preferred to bat first but played the game as it came. The 19-year-old captain said Botha played some crazy shots up front but knew what she was doing.
Coach Dinesha Devnarain said: “The moment is bigger than I could ever imagine. As a nation, I must give credit to Cricket South Africa, the policies that they have put in place, it’s easy to say, ‘what are we doing right now?’ but it’s probably due to things that have been done over the last five to 10-year plans.
“I don’t think it would have been possible without good guidance and good governance. For us, as an U19 team, in our second World Cup, most of these girls have never travelled out of the country, it’s been a rollercoaster, but talk about adaptability with a young group. What a moment, what a privilege and definitely what an honour. I’m the most thankful coach right now.”
The Proteas have gone undefeated in the World Cup and will play India in the final, in a repeat of 2023.