Sexton's tenacious on-field persona is often characterised as critical to his success as Ireland's stellar playmaker, but Best revealed the Leinster outside-half is just as central to team bonding as he is driving standards of play.

"Johnny is fully aware that World Player of the Year, winning big matches, it all comes about because of his rugby ability," Best told Press Association Sport.

"It's a short career, he's competitive, he wants to win things, and he knows the best way for him to win things is simply to be good at rugby.

"Johnny gets that. And that's all Johnny really wants to be; the best player he can be.

"He wants to be the best player in the world.

"He's achieved that with the award, but now he'll want to put two in a row, and then he'll say 'let's put three in a row'.

"Because he wants to be the best he possibly can."

Ireland will launch their Six Nations defence by hosting England on February 2, kick-starting a year ending with the small matter of the World Cup in Japan.

Sexton will be crucial to Ireland's chances of a successful 2019, and remains just as determined not to accept second-best from either himself or his team-mates.

That passion sometimes spills over into a harsh word to a colleague, or even occasionally a referee.

Sexton even clashed with Ireland team-mate Joey Carbery when Leinster lost out 26-17 in a feisty encounter at Munster on December 30.

But Best revealed Ireland are proud to benefit from – and happy to joke about – Sexton's single-mindedness.

"It's important that when you get onto a rugby pitch it's not always a reflection of what you're like off it," said Best.

"If you're a competitive person, you just want to win, and that's Johnny.

"People get fixated with Johnny shouting, but it doesn't happen often and it's only because he wants to be the best, and he expects that from everyone around him.

"In our squad, the fact that it's joked about means that people understand that. They get it.

"Nobody takes offence to it. Because firstly he probably knows better than anyone where everyone is meant to be.

"He's trying to make sure we are better prepared.

"And secondly it's because he cares if he wins. It would be worse if he said nothing, just got angry and didn't try to help anyone.

"He's very different off the pitch, he's in the middle of everything.

"It will be rare you go into the team room and he'll not be there, in the middle, joking and laughing with someone, or getting his rehab done, or whatever.

"But he'll always be in and around the team room, in the middle and messing.

"When the time comes to relax he can relax as well as anyone, he's got that balance and it's important to get that balance."

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