Possibility of dream pairing at World Cup

All Blacks, Sonny Bill Williams and Ma'a Nonu, celebrate a try by Sonny Bill. Photo / Alan Gibson.

It seemed a classic either/or scenario but the All Black selectors have decided they can solve the Sonny Bill Williams or Ma'a Nonu dilemma by including them both.

It's an intriguing solution to an intriguing problem. There are tough calls to be made in many positions, but the situation at second-five is quite different.

The All Blacks have two athletes the rest of the world would kill for in Williams and Nonu. The latter is in the form of his life, closing in on 100 test caps and a player who has barely put a foot wrong at test level in the past five years.

Williams is the perfect physical specimen with a range of skills possessed by no one else. His form was patchy throughout Super Rugby and he was quiet in Apia, but he's a player coaches find hard to resist.

Hard because at 1.94m and 110kg, he's the sort of athlete that can make just about anything happen. Hard because when he's at his best, he's a game breaker: his offloading and running ask questions of defences they can't answer.

At his best, he's world class and it would be nearly impossible to have to say which one of him or Nonu would be the right choice to start at No 12 for the All Blacks.

That decision hasn't had to be made for the Argentina test because the selectors have concluded that Conrad Smith would benefit from another week off.

Without Smith, the possibility of playing both Williams and Nonu together presented itself. It's not the first time they have been paired together: Williams made his debut in 2010 at centre with Nonu at second-five. They swapped jerseys the following year for the opening game of the World Cup against Tonga and were a partnership in the first two Rugby Championship tests of 2012 when Smith was injured.

Clearly, head coach Steve Hansen likes the potential of the partnership and what it brings. There's the incredible explosive power of their combination.

Imagine Williams driving into half gaps and a giant mitt popping the ball out of the contact for Nonu to smash on to. In a physical game all about collisions, those two are a dream combination in that regard.

There's also the defensive power they bring: the ability to intimidate ball carriers with their high impact tackling.

But what happens when Smith is available for selection? The Williams-Nonu combination has brawn aplenty but the All Blacks need the brain of Smith. They can't possibly think about playing knockout football at the World Cup without the calm and composure of Smith in the No 13 jersey. They can't smash their way to glory. They need Smith's deft touch: his defensive reading, distribution and strong leadership.

To even think about leaving him out would be madness - as surely every New Zealander knows the price of going to a World Cup and then making a random decision about who to play at centre.

Hansen, who hasn't put a foot wrong yet, is unlikely to be seduced by the Williams-Nonu combination. What he and his fellow selectors will be looking for on Friday night is confirmation that Nonu and Williams are a valid option: a combination to have up the sleeve as it were.

The All Blacks want to build multiple options and if they see that Williams and Nonu can be destructive and effective, it's a weapon to store.

The tough choice on whether to start Williams or Nonu will still have to be made at the World Cup - but it might be that for that the two of them are on the field together for the final half hour of the biggest games.