Rugby World Cup 2015 - Australia v Argentina: How the Pumas got it wrong

Referee Wayne Barnes shows the yellow card to Argentina lock Tomas Lavanini. Photo / Brett Phibbs

Argentina have come to grips with the Rugby Championship but have some way to go to comprehend World Cup rugby.

They got it so wrong when they fronted the Wallabies in the semifinal today. The inquisitions and findings will emerge about whether the Pumas struggled with the occasion, their temperament or were acting under instructions.

But their template for knockout rugby was badly askew and they were struck out of this year's race for the Webb Ellis Cup after ceding a massive start to the Wallabies.

The Pumas played most of the opening quarter of rugby down their end of Twickenham and when they made mistakes, the Wallabies punished them.

A 29-15 victory to the Wallabies has set up a trans-Tasman conclusion to this eighth World Cup, where the only unbeaten sides will vie to become the first nation to win three global crowns.

It will be the first time the All Blacks and Wallabies have met in a World Cup final, an extra chance to sort out this season's bagging rights after they split the Bledisloe Cup tests in Sydney and Auckland and a battle between the top two sides in the world.

It's a script many forecast if the Wallabies could get through their group. They escaped that squeeze against England and Wales and then a controversial late win over Scotland.

In their semifinal they squeezed up hard on the Pumas and benefitted from their flustered response. Twin converted tries inside 10 minutes was a massive boost for the Wallabies and while the Pumas looked likely at times they could not crack the Wallaby lines throughout the test while their rivals added another two tries.

Victory has given rookie international coach Michael Cheika and his team a chance on Sunday to cement a remarkable turnaround in Wallaby rugby. He and his team would celebrate this game before they worked out how to win against "a pretty dynamic (All Black) team."

Wallaby pressure told early when Rob Simmons intercepted an audacious in-ball before Adam Ashley-Cooper scored on each wing after gaffes from the Pumas who also lost lock Tomasi Lavanini to the sinbin for an illegal tackle.

It was another in the catalogue of questionable decisions made at this tournament but referee Wayne Barnes and the TMO were insistent. Everything worked for the Wallabies except their scrum as replacement loosehead James Slipper struggled to contain his opposite.

David Pocock returned from injury to dominate the breakdowns once more while the decisions from Will Genia and Bernard Foley were crisp. They saved the Wallabies late in the half with covering tackles when the Pumas looked certain to score.