All Blacks assistant coach Ian Foster has fired the first shots in the expected war of words with the Springboks - warning the South Africans against getting "too smart" ahead of the sides' mouthwatering World Cup opener.

Speaking to Sky Sport after the All Blacks' first full training session in a sweltering Kashiwa, about 60km outside Tokyo, Foster suggested the Boks were playing mind games with their tactic to deliberately give up the ball for large parts of their final warmup match against Japan at the weekend.

The Boks defeated the Brave Blossoms 41-7 despite only having 36 per cent possession - a tactic head coach Rassie Erasmus later admitted was employed to prepare for the All Blacks clash next Saturday.

While Foster called it a "smart move" he warned that the strategy could backfire when the sides meet in the International Stadium in Yokohama.

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"You don't really know whether they were doing that deliberately or whether it's part of their tactics. They're a team that kicks well and kicks a lot it, while Japan is very aggressive with their line speed, so it certainly wasn't a bad tactic against the Japanese," Foster said.

"It was probably just a smart move from them, trying a different part of the game [but] what you've got to try to make sure in this business, is that you don't get too smart - you work on one area only to get caught out in another area.

"It's hard to play [mind] games in pre-World Cup games but we know they will be 100 per cent prepared in a week's time. We've got to make sure we are."

All Blacks assistant coach Ian Foster and head coach Steve Hansen. Photo / Photosport
All Blacks assistant coach Ian Foster and head coach Steve Hansen. Photo / Photosport

The All Blacks wouldn't stray from the attacking game plan they implemented against a dreadful Tonga in Hamilton, Foster said.

"I won't give you too many specifics, but what I can say, is that we have a game we've been trying to develop and been growing. We like to attack, we like to play with ball in hand and for us, the challenge is the skill level and decisions we make there and also the choices we make of when to do it and when not to do it.

"All Black rugby - we play a fast game and that won't change."

Richie Mo'unga, who missed the 92-7 thrashing in Hamilton through injury, is on track to reclaim the No 10 jersey against the South Africans.

"He's tracking really well. Last week we pulled him out more [as a] precaution, so this week is about him graduating back into full training and we expect him to be fully fit and available."

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Asked about facing one of the pre-tournament favourites first up, Foster said the All Blacks wouldn't have it any other way.

"We love the draw because it's meant that we've turned up and there's no excuse, no waiting around ... it's right there in front of us," he said.

"We're about to face a very confident South African team but they're going to face a very determined All Black team and it's a great way for the tournament to get under way."

The All Blacks also face Canada, Namibia, and Italy in pool play before a likely quarterfinal clash with Scotland or Ireland.