The 2015 Rugby World Cup final will be a trans-Tasman affair after Australia topped Argentina 29-15 on Sunday.

A hat-trick of tries from Adam Ashley-Cooper backed by the hard work of David Pocock, Michael Hooper and former Kamaishi Seawaves flanker Scott Fardy saw the Wallabies set up an Oct. 31 clash with the All Blacks, in a game that will determine the first three-time world champion.

Ashley-Cooper may have grabbed the man-of-the-match award but his three tries all came on the back of some brilliance from his teammates — a good cut-out pass from Bernard Foley, a delightful floated pass from Matt Giteau and a superb break from Drew Mitchell.

Meanwhile, Pocock and Hooper dominated the breakdown, forcing a number of turnovers and Fardy covered every inch of the field and then some, tackling the Pumas to a standstill.

"The back row went well. It was a good shift by those boys," said Australia coach Michael Cheika. "Scott really knew when to come in and make the tackles. It was Michael's 50th cap and he was excellent and it was really important to get 80 minutes from David."

It was a point not lost on Argentina coach Daniel Hourcade.

"They dominated in the breakdown. We dominated in the second half but we didn't get any tries. If we had got a try then I think we would have won the game."

Conditions at Twickenham were very different from the day before when the All Blacks out-slogged the Springboks in the rain. And the rugby was too, as the war of attrition between the sport's greatest rivals was replaced by a more open affair that had the house rocking under the blue sky.

But it was Argentina's willingness to run everything that proved to be its undoing as it was chasing the game from the very start after Rob Simmons scored with a simple intercept just 68 seconds into the game.

"I just happened to be in the right spot," Simmons said. "I don't think I am in the right position to get too many but I was lucky enough to be in the right position today."

Australia did its bit to keep the Pumas in their game, giving away seven first-half penalties, three of which Nicolas Sanchez banged over.

But the Wallabies also scored two other superb tries through Ashley-Cooper, the second after Tomas Lavanini had rather harshly been sent to the sin bin, and two conversions from Foley, who will join Ricoh Black Rams after the tournament, made it 19-9 at the break.

The second half saw the boot dominate early on as far as the scoreboard was concerned with Foley adding one penalty and Sanchez two.

But that didn't mean any shortage of running rugby to thrill the crowd of 80,025. Both sides though were defending heroically and the bodies strewn across the field at nearly every stoppage was evidence of the work and bravery put in.

"We tried everything but we couldn't score a try," said Argentina defense coach Pablo Bouza.

Australia tried everything too and in the end it was Mitchell's brilliance that helped seal the game, the wing producing a great 50-meter run before feeding Ashley-Cooper for his third, eight minutes from time.

"I don't think Drew understands what he's doing himself sometimes," said Cheika. "Seriously, he's a good footballer. He was excellent."

Foley once again added the extras and while the Argentine fans never let up the noise — some 25,000 were said to be in attendance — it was obvious from the tears in the coaches' box that it was game, set and match to the Wallabies as they set up the first ever trans-Tasman World Cup final.

"I haven't really thought about it," said Cheika. "Tonight we have given ourselves the opportunity to play in a World Cup final and we'll work out how we are going to do it against a pretty dynamic team."

The Pumas, meanwhile, have to lift themselves to take on the Springboks in the bronze-medal game.

"We have to get over this defeat and start again. We will concentrate on Friday. We want to be in the Top 3 of the world," said captain Agustin Creevy.