Talk of two-time defending champions New Zealand being vulnerable as they bid to make Rugby World Cup history will be music to the ears of Steve Hansen.

The All Blacks start their quest to lift the Webb Ellis Cup for an unprecedented third time in a row as favourites, and rightly so.

Yet New Zealand are not the all-conquering force that have taken on all comers for so many years and slipped to second in the rankings behind Ireland ahead of the tournament in Japan.

Chinks in the armour were exposed during a Rugby Championship campaign that New Zealand finished in third spot after they were soundly beaten by Australia and drew with South Africa.

The Springboks were crowned champions, making a strong statement just six weeks before the two heavyweights do battle in their Pool B opener in Yokohama.

Ireland have beaten Hansen's side twice in the last three years and South Africa consigned them to defeat in a Wellington classic 12 months ago.

The juggernaut has been halted, but there is no doubt it can fire up driven on by inspirational captain Kieran Read - hungry to end his international career by lifting the famous trophy yet again in November.

Australia were put in their place a week after rocking the 14-man All Blacks in Perth, going down 36-0 at fortress Eden Park just eight days later.

Hansen must be rubbing his hands together reading or hearing about his side being fallible as they prepare to try and make history and give him the perfect send-off.

The All Blacks supremo declared Ireland are favourites to dethrone New Zealand after his side were beaten in Dublin last year, but sounded a warning upon arrival in Tokyo.

"To try and do things that have never been done before is a hallmark of what New Zealand people are about." he said.

"We came away from the home shores and settled in a country at the bottom of the earth. We had to find ways to live in isolation when life wasn't like it is today.

"They became pioneers. That's important in life and particularly in sport; you've got to strive to be leaders rather than followers. We have an opportunity that no one else at the tournament gets; we can shy away from it or get really excited about it. We are really excited by it."

One look at the list of New Zealanders who failed to make the squad shows the challenge their rivals face in trying to end their dominance.

Test centurion Owen Franks was sensationally omitted along with outstanding centre Ngani Laumape, highlighting the embarrassment of riches at Hansen's disposal.

Liam Squire is also absent, but Hansen has such an abundance of quality to call upon that New Zealand remain the team to beat.

The fear factor may not be what it was, but write the All Blacks off at your peril.