A crestfallen Willie Tonga admitted he was shattered at the disastrous manner his North Queensland career ended after the Cowboys were blown away 42-8 by Manly in Saturday's NRL qualifying final.

The Queensland and Australia centre, who joins Parramatta next season, revealed he struggling to comprehend how his side managed to concede 42 points in 32 second-half minutes at the Sydney Football Stadium, having dominated the first period.

"It is surrealto think that it's all come to an end. This result was really unexpected, we'd had a good week, trained well, it just wasn't our night," Tonga said.

"We felt really good at halftime, we had momentum at the start of the second half, but we sort of slipped off, missing tackles around the middle and they made us pay for it."

The complexion of the game changed in the 47th minute when a Johnathan Thurston pass intended for Matt Bowen missed the target with the Cowboys in good field position and was regathered at the visitors' 10-metre line by Shane Rodney.

Four plays later, Will Hopoate dived over for a try to visibly lift Manly as they seized the initiative and ran away with the game, and Tonga admitted it was the turning point.

"They are a really good team and you can't afford to give a team like that an opportunity so easily. They are always going to be tough to beat and you can't give them a helping hand," he said.

"I am bit stuck to think where it went wrong. It is all a bit of a blur and tough to take.

"I am looking around at the boys' faces and thinking this is the last time I will play alongside a lot of them.

"But the future of the club is good, there are a lot of young players here and, although my time here is now over, the club has a lot to look forward to."

Cowboys coach Neil Henry was at a loss to explain why his side capitulated after halftime but was full of praise for Manly.

"We controlled the game for the first 40, we played some very good footy but seven unanswered tries is pretty hard to discuss how it happened," Henry said.

"It was pretty comprehensive in the end which is disappointing. They were able to maintain their focus for 80 minutes and we weren't.

"They've (Manly) built a season on being able to play 80 minutes and are a very good side.

"There are no excuses. The way we opened up at the back-end is a disappointing way to finish our season ... it's a bit of a nightmare really."

On a difficult night for the Cowboys, the club was boosted by news that the neck injury sustained by Cory Paterson was not as bad as first feared.

Paterson was rushed to hospital with a suspected cracked vertebra, but scans have revealed only ligament damage.

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