Why All Blacks losing to Springboks would be bad omen for what's to come

Saturday's Rugby World Cup showdown is shaping up to be tournament defining for the All Blacks. 

Beat the Springboks, and they will almost certainly top Pool B, but lose and they would have to become the first team to win the Web Ellis Cup after dropping a game.

It's a world away from New Zealand, as All Blacks fans catch the Shinkansen bullet train across town to Yokohama stadium - an hour-long trip done in 12 minutes.

A fast start is fun for fans travelling at the World Cup, but it is also crucial for the All Blacks' campaign after coach Steve Hansen's men were more like an Auckland traffic jam than a bullet train early in the rugby championship.

"We are notorious slow to start seasons when we come together. Our last games will be a better reflection on where we can play," says Hansen.

After the draw in New Zealand against the Boks and the hammering in Perth versus the Wallabies, they found top speed with big wins against Australian and Tonga. The All Blacks are confident the foot will remain on the gas.

The All Blacks and the Springboks are two all at World Cups, but more importantly, there have just been two points between them in their last three clashes, as the All Blacks' potent attack found its equal in the Boks' defence-first approach.

It is a titanic clash, so what better way to kick off the World Cup than with the scalp of your greatest foe.

It might only be pool play, but the All Blacks are flying head-on into one of their biggest World Cup challenges.