New Zealand five-eighth Benji Marshall put the Kangaroos on notice by declaring his fragile body was in the best shape of his career heading into Sunday's World Cup opener.

Marshall's stop-start representative career will be all go when he lines up for the Kiwis against Australia at the Sydney Football Stadium, the mercurial Wests Tigers star central to New Zealand's hopes of springing an upset.

The 23-year-old claimed the World Cup had been in the back of his mind for "probably five years", the end-of-season tournament the first time Marshall has been available for the Kiwis in the back half of the year since making his Test debut in 2005.

"I've got a big role to play in this team, playing in the halves as well, I'm reasonably confident that I can do the job," Marshall said.

"I know it's going to be a big ask this week against Australia, but I've prepared the last few weeks and it's probably the best I've felt.

"It's been a pretty long six weeks (since the Tigers bowed out of the NRL competition). While everyone else has been playing, I've been training pretty hard.

"It's been good being on the field for a few games in a row and having the opportunity to represent New Zealand at the end of the year for a change instead of just the Anzac Test - to be able to play in the World Cup at the same time, it's big deal for me."

Marshall was named by coach Stephen Kearney in the No.6 jumper with Wigan playmaker Thomas Leuluai by his side at halfback.

Rookie Melbourne forward Sika Manu won a place in the starting side, Manu part of a powerful back row along with Simon Mannering and Jeremy Smith.

There was no room for Parramatta centre Krisnan Inu, with South Sydney pair Issac Luke and David Fa'alogo also overlooked.

Marshall said the Kiwis were confident of putting in a good show on Sunday despite the fact most critics have written them off following the loss of influential trio Roy Asotasi, Frank Pritchard and Sonny Bill Williams.

The loss of Williams in particular - following his mid-season defection to rugby union - means even more of the spotlight on and off the field has become fixed on Marshall.

"I know I've got a lot of good teammates around me that can do the job as well," Marshall said.

"If they're just worrying about me, it will relieve the pressure off a couple of other guys as well - that'd be alright, I've got no dramas with it.

"A lot of people are saying we're right-offs, we're going to be a pushovers. We don't believe that. We've got a lot of belief in ourselves."

Marshall also claimed that what the Kiwis had lost in playing strength had been more than made for off the field with Kearney and Wayne Bennett forming a powerful brainstrust.

"Having blokes like Wayne Bennett and Steve Kearney in camp, they bring a lot of discipline which I think maybe we've lacked in the past in the Kiwi camps," Marshall said.

"It's been good. I've learned a lot off both of them and you can just tell the professionalism that they both hold at their clubs that they bring here and it rubs off on everyone else."

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