Stephen Larkham insists Australia will face the greatest fly-half of all time when they clash with New Zealand in Saturday's World Cup final at Twickenham.

Dan Carter will make his 112th Test appearance for the All Blacks when the world champions seek to become the first team to defend their crown by lifting the Webb Ellis Cup for an unprecedented third time.

The 33-year-old may no longer be the magician who left the British and Irish Lions spellbound in 2005 but backs coach Larkham - himself a distinguished former fly-half - believes his position among the all-time greats is already guaranteed.

"Dan Carter will be number one in the pantheon, clearly number one," said Larkham, a Test centurion who steered the Wallabies to World Cup glory in 1999.

"Probably over here in England Jonny Wilkinson will be number one, but in the southern hemisphere Dan is ranked number one.

"He's shown really good composure during this tournament. His skills haven't dropped off at all, he picks and chooses when he wants to run and he does that really well. He's combining with his team-mates very well."

Carter will conduct the final performance of New Zealand's world title defence against a team they routed 41-13 in Auckland during the summer, but only having succumbed 27-19 in Sydney a fortnight earlier.

The Wallabies have undergone a remarkable transformation since head coach Michael Cheika inherited a dysfunctional squad beset by disciplinary problems and reeling from a split between players and management which had opened up during the 2014 Rugby Championship.

Having emerged from the toughest pool in World Cup history by toppling England and Wales - the former despatched in record-breaking fashion - they stand one win away from seeing Australia recognised as the competition's most successful nation.

"The most important thing we've given the team over the last 12 months is a bit more structure," Larkham said.

"From all reports, game plans were being changed from week to week, as were the defence and attacking styles. But ever since Cheika came on board there's been a real clear direction.

"We've had a difficult run to this final - pretty much every game has been final week - so we know what we need to do in terms of preparing for a big game.

"We've scored some good tries but defence is going to be the key. Games against New Zealand can go all over the shop, sometimes they open up, sometimes they close down.

"We haven't got a plan either way. We are going in there with a plan on how we want to play, and then it comes down to how it is refereed and the conditions."