Rugby World Cup 2015 final - All Blacks v Australia: Bench talent will determine World Cup winner

Sonny Bill Williams. Photo / Getty Images.

It's New Zealand v Australia, the two best teams in the world, in the World Cup final.

And a big reason for that in my opinion is the depth of talent both nations have, but, in particular, the talent they have on the reserves bench.

What was really obvious to me today during Australia's win over Argentina was the depth of talent on their bench. The minute Argentina started to leak injured players - quality players - in Agustin Creevy, Juan Martin Hernandez and Leonardo Senatore, they couldn't cope.

One of the big reasons why the All Blacks won against the Boks was the impact provided by their bench, and Australia have similar depth at the moment (they never used to). Ben McCalman, Kurtley Beale, Matt Toomua, even Nick Phipps when he came on at halfback and provided the pass to Drew Mitchell for Adam Ashley-Cooper's third try - they all added something.

Neither Argentina nor South Africa had that impact. Pat Lambie kicked a goal, yes, but I can't think of other reserves making an impact for either team.

As much as I'm a rugby purist and love the best XV against the best XV match-up, the game has changed. Now your bench and the way you manipulate substitutions is a big part of the way the modern game is played.

On the All Blacks, I don't believe they should bother analysing their victory over the Boks too closely. They got a few things wrong - I thought they kicked away too much ball. But, ultimately, their perseverance won them the game. They stuck by what they thought would beat the Boks and it did.

It was a grind, and my feeling after the game was one I haven't felt in a long time after an All Blacks test - relief. The last time I felt that was probably the World Cup final of 2011, a match they probably didn't deserve to win. However, there was no doubt the All Blacks deserved to beat the Boks at Twickenham.

They got into an arm-wrestle and they didn't want that. Credit to the opposition, they worked out how to slow the ball down - they hit them high and put them under pressure.

But two tries to none and also the way the All Blacks created pressure was the winning of the game. The Boks spent no time pressuring the All Blacks' line. None, zero. They couldn't create phase play past six or seven phases and that's what the game boils down to.

As I say, I believe it would be detrimental to analyse that game too closely. They need to look forward. They just need to say, we're in the final, we've beaten South Africa, who are the third best team in the world and now we have to beat the second best team in the world - Australia.