'It's hard to beat' - Wallabies great Phil Kearns believes two teams can prevent an All Blacks World Cup hat-trick

South Africa impressed in claiming the Rugby Championship although Kearns reckons their campaign could be on shaky foundations given the cloud over talismanic lock Eben Etzebeth.

Former skipper Etzebeth is being investigated by prosecutors over his involvement in an alleged assault and racial abuse during a bar brawl last month.

"With South Africa, I think Etzebeth is a critical player so depending on what happens with him will be important for their chances," Kearns told AAP.

"But I just think the size of England and South Africa is going to be a difficult thing for teams to overcome.

"Both of them aren't lacking pace either, so when you've got those physical capabilities it's hard to beat."

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Veteran coach Steve Hansen believes his All Blacks can overcome the inevitable suffocating defensive screens their opponents will erect.

He has played two trump cards in the lead-up, fielding dynamic pair Beauden Barrett and Ardie Savea out of position at fullback and blindside flanker respectively.

Both are potential tournament stars in a team whose high octane game plan has been designed with the firm grounds and hot conditions in mind.

"I think there's definitely been a swing or bias towards defence," Hansen said before his team left for Tokyo.

"But someone's going to crack that nut – the defensive nut that needs to be cracked – because history tells us that will happen.

"When it does then it will open up the floodgates for the attacking game to become strong again."

The size versus speed debate will get an early airing when the All Blacks and Springboks meet in Yokohama on Saturday in a highly anticipated pool opener.

Some patchy All Blacks form over the past two years has stripped them of the top ranking and eroded the aura they enjoyed at the 2015 event.

For that reason, the tournament is rated the most open in recent memory, with regular visitors to the knockout stage such as Australia, France, Scotland and Argentina also among those who can't be discounted.

The dark horses are Fiji and Japan, with the hosts handed the sort of stage World Rugby has craved as it battles to expand its footprint in a potentially lucrative marketplace.

AAP

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