They will face Argentina in the final in the coastal town, the first World Series event in Spain.
South Africa started strongly and never took their foot off the pedal against Australia. They kept possession well and applied pressure, which led to the Aussies conceding an early yellow card for repeated infringements on defence.
Staying calm and calculated, the Blitzboks kept working both sides of the field until JC Pretorius ran in untouched. Branco du Preez converted for an early 7-0 lead.
The men in green and gold did not allow Australia to get into any sory of pattern with some solid hits, and from such a crash tackle by Du Preez, the ball was turned over and in a flash, Mfundo Ndhlovu scored in the corner to extend the lead.
Leading 12-0 at the break, the second half saw more of the same from the Blitzboks. Coach Neil Powell started to use his bench players and they kept up the relentless pressure. From yet another sustained attack, Selvyn Davids waltzed over the line.
The final against Argentina is at 19h56.
South Africa 19 (12): Tries - JC Pretorius, Mfundo Ndhlovu, Selvyn Davids. Conversions: Branco du Preez (2).