The winner will play New Zealand in next weekend's championship decider but with the outcome of the second match still very much uncertain.
Australia, World Cup champions in 1991 and 1999, are attempting to reach the final for a fourth time while the Pumas are bidding to reach the final for the first time.
Normally, the Wallabies would be overwhelming favourites but Argentina, one of the most improved teams in world rugby, are the strong sentimental favourites with Diego Maradona in the stands leading their supporters.
Argentina have made one change to their team, bringing back outside centre Marcelo Bosch from a one-week suspension which saws him miss the impressive 43-20 demolition of Ireland in the quarter-finals.
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“To manage my anxiety is important, I’m going to play the most important match of my life, a World Cup semi-final” Bosch told Reuters.
“So I try not to drive myself crazy, not to play the match beforehand (in my head) already dreaming how the match might be.”
Australia have made three changes to their starting lineup. David Pocock and Israel Folau were both recalled after passing last-minute fitness tests.
The pair, key players for the Wallabies, missed last weekend's heart-stopping quarter-final against Scotland because of injuries but were cleared to return the starting lineup making it through training on Friday.
There was one casualty from the Scotland game, however, with loosehead prop Scott Sio failing to recover from an elbow injury.
Sio, instrumental in helping restore confidence to Australia's wonky scrum, was replaced in the starting lineup by James Slipper, who earns his 73rd test cap, a record for an Australian prop.
Australia coach Michael Cheika said he expecting a tough match.
“We’re not surprised at all about their position here,” he said. “So we’ve been preparing accordingly.”
(Editing by Julian Linden)
