Backline linchpin Berrick Barnes has set himself the massive, yet crucial, task of bottling up fearsome All Black Ma'a Nonu from the outset in Saturday's trans-Tasman clash.

While Barnes holds a key for a Wallabies upset with his canny ball-playing and kicking game outside Matt Giteau, the inside centre underlined the importance of his defence against Nonu on his Westpac Stadium home ground.

The NZ powerhouse, who enjoys a 16kg weight advantage over his Australian opponent, moves to his preferred No.12 position with Stephen Donald dumped, leaving classy five-eighth Dan Carter as the sole Kiwi playmaker.

With Nonu and the similarly-sized Isaia Toeava teamed together in the midfield, the All Blacks backline attack looks more predictable but Barnes is wary of their destructive ball-running.

The 23-year-old may be Australia's Mr Reliable in defence but he hasn't always enjoyed his tussles with Nonu, either at Super 14 or Test level.

Barnes said he couldn't afford to allow the rampaging 104kg Hurricanes centre to settle in quickly and get his confidence.

"Ma'a presents a challenge," he said. "You know if you don't get on top of him early you're going to have a long night.

"If their forwards are going forward and he's on the front foot, he's one hell of a tough guy to stop.

"I give away almost 20kg to the guy and you've got to get up in his face."

Barnes doesn't need to be reminded of the dangers of Nonu's tackle-breaking midfield runs.

He has spent almost the entire Tri-Nations battling a painful hip injury inflicted by Nonu in the series-opening 22-16 loss in Auckland.

"My hip didn't recover for about six weeks after that," he said. "I was still playing but it was sore. I'm good to go now.

"When he gets you, they stick too. You know what you're going to get and we've had some good battles over the past couple of years."

NZ would have undoubtedly seen the Wallabies midfield defence can be exposed, with Springbok centres Jean de Villiers and Jaque Fourie making a string of line-breaks in their two recent Tests in Australia.

Not only is Barnes on guard against his direct opponent, centre partner Adam Ashley-Cooper is also concerned about the impact 23-year-old call-up Toeava can have at No.13.

"He absolutely cut us up this year at Canberra Stadium when the Blues played the Brumbies," Ashley-Cooper said. "He's a strong attacker and very deceiving. Great feet and great with the ball in hand.

"So I guess opposing him in defence I'll really have to work with the guys inside and outside me so he doesn't make me look stupid."

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