Tokyo - New Zealand coach Steve Hansen has insisted it "won't be the end of the world" if his reigning champions lose their opening Rugby World Cup blockbuster against South Africa.

Every team that has won the World Cup has been unbeaten and Saturday's Pool B clash between New Zealand and South Africa in Yokohama promises to be one of the games of the tournament.

"Clearly this is a big match because it's the All Blacks v South Africa, which is traditionally a massive match anyway," Hansen told reporters at New Zealand's hotel in Tokyo on Monday.

"Logic will tell you whoever wins this game, probably wins the pool.

"But as we found it in 2011, you don't have to necessarily win the pool to get into the final. France did it the other way," said Hansen ahead of the All Blacks' bid to lift an unprecedented third successive World Cup.

"It's not the end of the world (if you lose), and it doesn't mean you are going to win the World Cup or get into the final because you win this game. There's a lot of water to go under the bridge."

New Zealand and South Africa have won five World Cups between them and the form of coach Rassie Erasmus's resurgent side, this season's Rugby Championship winners, has heightened expectations.

The last three All Black-Springbok encounters saw a draw and one win each, by just two points both times.

"Both teams are pretty close," said Hansen.

"Over the last three games, they won, we won one on the death knell and they drew one on the death knell.

"Their defensive system has changed a lot (under Erasmus). They roll the dice big time - their wingers come in off their wings. And they're good at it, very, very good at it.

"You want them to roll a couple of ones, rather than a pair of sixes."

Hansen said his squad understood the danger of expending too much emotional energy bin the build-up.

"There's a big Test match, a big box of chocolates at the end of the week. You can't eat them on Sunday because there will be none left for Saturday," he said.

"The players are aware of that. You can't play it Monday, Tuesday or Thursday, you've got to be ready to play Saturday."

South Africa, with a backdrop of rows over post-apartheid transformation, have endured some painful results since a shock defeat by Japan at the 2015 World Cup, including a 57-0 thrashing by New Zealand at North Shore City two years ago.

But Hansen said their current form was a return to their normal standards.

"I'm not surprised," he said.

"Every time we've played them, other than once in North Harbour when we had a day out of the box, the games have been reasonably hard-fought and tight.

"They've gone through some challenging processes but I think they are starting to reap the rewards of that now. They are selecting a team on a genuine basis that they are all good enough to be there."

Recent typhoons in Japan have emphasised how handling the ball well in wet conditions could be important at this World Cup.

Wales coach Warren Gatland has been oiling up training balls to make them slippery, and Hansen had a cheeky exchange when reporters told him of the practice.

"You want to rephrase what you just said?" asked Hansen.

"You said 'Warren Gatland has been putting baby oil on his balls'. That's probably not the headline you want.

"We've just been using plain old water. It seems to be working all right."