Winger Adam Ashley Cooper's hat-trick of tries sent Australia into a first World Cup final since 2003 after a 29-15 victory over Argentina on Sunday secured a showdown with holders New Zealand at Twickenham next weekend.
The Wallabies were superior at the breakdown where David Pocock was immense and too clinical in the backline for the gung-ho injury-hit Pumas who paid the price for costly early mistakes.
Australia, in control from two early tries, were under the cosh for long periods of the second half but resilient defence and Ashley-Cooper's third try on 71 minutes put the game beyond reach.
"It was a tough game and we knew it would be. We had to defend a lot. That took a fair bit out of the tank," said Australia captain Stephen Moore.
Coach Michael Cheika added: "What we did was let the game open up which suited them. We had to work hard to stop them from scoring a try. We can improve again and that's really important now."
Saturday's match will be the first time the southern hemisphere powers, both world champions on two occasions, have met in a World Cup final having clashed in three semis.
The only final not to feature either New Zealand or Australia since the tournament's inception in 1987 was eight years ago when South Africa beat England.