Sonny Bill Williams is under orders to stick to the game plan when he returns to the All Blacks starting line-up in the World Cup opening match against Tonga on Friday.

Williams has been sliding off the selectors' radar lately, so much so that he could not make the bench against Australia two weeks ago, but has been brought back for the World Cup opener in a surprising midfield reshuffle.

Automatic first-choice inside centre Ma'a Nonu has been shifted out one place to make way for Williams with Conrad Smith pushed out of the squad altogether.

However, the recall of Williams has come with a proviso from coach Graham Henry who said the Rugby League convert was being given a chance to prove himself.

"The reason for the selection was to give Sonny Bill an opportunity and he's got that," he said at the team announcement.

"We don't know what's going to happen later in the tournament and who's going to be standing and who's not so we've got to give players an opportunity to play and to force their abilities on the selectors."

He added Williams has been given the message about what was expected of him: "Don't try to do it all in five minutes, the game lasts for 80," he said.

"I think players are inclined, when they do get a chance and they haven't played for a while, to try and push it too much, probably overdo it.

"I guess patience is going to be the key and if he does that and lets his natural abiity control the way he plays, I think he will play well," said the All Blacks boss.

Williams refused to be drawn on his drop off in form this year, in which he started in only one of the five All Blacks Tests.

"Everything else is irrelevant to me" he said before deflecting further questioning about his form by repeating he was "excited" to play Tonga.

"I'm excited, really excited. I don't know how many times you want me to say it."

Standing outside Dan Carter and against minnows Tonga, Williams has every opportunity to shine with his back-of-the-hand off loads putting Nonu into space.

But a below par performance may not help his options as he weighs up his playing future after the tournament.

The World Cup "is going to define this team and the people associated with it," Henry said.

SAPA-AP