North Melbourne coach Dean Laidley entered into the spirit of World Youth Day on Friday night, saying "peace be with you" at the end of his media conference.

If he is indeed a religious man, Laidley could well have gone to bed muttering a quiet prayer of thanks for Drew Petrie.

The Kangaroos are back in the AFL top eight after their outstanding 18-point win over Collingwood at Telstra Dome and Petrie's game was pivotal.

The North ruckman took 11 marks, kicked two goals and had 26 hitouts.

But more than those impressive statistics, he was everywhere - helping out the tall defenders, dominating the centre bounces and providing North with a tall target in attack.

He earnt strong praise from Laidley and Collingwood coach Mick Malthouse, although Malthouse's comments dripped with bitter sarcasm about his own side's poor night.

"We had two ruckmen, rucking against a centre half-forward, and the centre half-forward has probably been best on the ground, second-best on the ground and third-best on the ground, I reckon," he said.

Malthouse also ruefully noted that of Petrie's 11 marks, probably seven were the result of kicks from Collingwood players.

Laidley said Petrie was developing into a genuine star for the 'Roos.

"It was super, he's pushed himself to another level - one of the true leaders of our footy club now and he's just willed his influence on the game," Laidley said.

"He's pretty much done that all year, he has been super."

Petrie's starring role also highlighted the absence of Collingwood's No.1 ruckman Josh Fraser, who continues to recover from a knee injury.

Fraser is playing in the VFL, but he is not yet able to ruck because of the knee problem.

"Until he starts to jump, the doctors allow him to jump, he won't be mysteriously played because we've lost today," Malthouse said.

"He's out because of an injury, he's not out because we can't find a spot for him."

While Collingwood led by 13 points at half-time, and looked capable of taking the game away from North, Malthouse was worried from the start.

"It was one of those games (where) I worried from the moment the ball was bounced until ... into the last quarter," he said.

"They had us and they were going to win (by) anything from three goals to 10 goals."

Collingwood have a potentially dangerous game next Saturday against Essendon, while North play bottom side Melbourne.

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