Ross Karl: Why Richie Mo'unga, Beauden Barrett must start for All Blacks ahead of Rugby World Cup

OPINION: This is the trial many rugby fans have been waiting for.

If it works, squeezing playmakers Beauden Barrett and Richie Mo'unga into the same starting 15, in Saturday's Springboks test in Wellington, could be a masterstroke in World Cup year.

We know Barrett is a very good fullback, so it makes sense to combine him with Richie Mo'unga at ten.

Leaving Mo'unga on the bench, behind Barrett, just doesn't add up anymore, especially when you can create a back three as venomous as Rieko Ioane, Ben Smith and Beauden Barrett.

Mo'unga deserves to start, after guiding the Crusaders to three straight Super Rugby titles.

You could make a strong argument that he's as good a first five as anyone in the world - just look at how castrated the Crusaders look when he's not there.

His ability to switch between kicking and running games is perfect for test level.

Now, I know there are naysaying Kiwis when it comes to shifting players out of their normal position in World Cup year, to fit in the most talented men.

But this is not Christian Cullen at centre in 1999. Barrett has already won a World Cup as an impact player at fullback. 

First-fives spend much of their time at the back anyway in the modern game. Tactical awareness and kicking is vital when the game morphs into a test version of school-yard force-back. 

Let's face it, Barrett's counter-attack is world-class. His cover defence is too.

Let's be honest, the back three was a worry if this tactic wasn't adopted.

Jordie Barrett, Sevu Reece, George Bridge and Braydon Ennor just don't provide the polish of an Ioane, Smith and Barrett back three.

 Ross Karl: Why Richie Mo'unga, Beauden Barrett must start for All Blacks ahead of Rugby World Cup

Jordie Barrett has a massive boot and plenty of raw potential but rewind 12 months, to the last Boks test in Wellington, and his compulsion to attempt risky plays is dangerous.

Sevu Reece has attacking brilliance but can't bring the all-around game of Ben Smith at 14.

George Bridge and Braydon Ennor have potential but are inexperienced.

Playing Mo'unga and Beauden Barrett also means the All Blacks no longer needing a ten on the bench. The reserves can now be stacked with x-factor midfielders and wingers.

Mo'unga at 10 and Barrett at 15 is the perfect mix. There's no good reason this shouldn't work.

Now... who'll be doing the kicking?

Ross Karl is Newshub's rugby reporter.

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