Newcastle has already qualified for the play-offs but were given a timely reminder on Saturday night at the Sydney Cricket Ground of how far off the pace they actually are from the premiership heavyweights.

The Roosters' 42-12 thrashing highlighted the gulf in class that currently exists between the two sides and the huge challenge in front of the Knights to try and bridge the gap.

The heavy defeat also leaves Newcastle anchored to seventh spot on the ladder and under pressure to win their final two competition games against St George Illawarra and the in-form Gold Coast Titans to have any chance of locking down a home semifinal in the first week of the finals.

They could be forced to take on the Dragons without hooker Kurt Mann, who is facing a one match ban after being charged with a crusher tackle.

The Knights may opt to fight the charge as he will only miss a game even if he loses the case.

O'Brien conceded the Roosters were on another level but admitted to being "shocked" at the breakdown in his side's defensive structures that saw the Luke Keary-inspired defending premiers pile on 24 unanswered points in the opening 21 minutes.

"The execution of our defensive systems and our contact in defence just wasn't there," he said.

"That really shocked and disappointed me the most about the performance.

"The thing with us at the moment is we can be really good one week and really poor the week after. There is just too big of a gap between our best and our worst.

"That has to change if we are to give ourselves a genuine chance. The lack of consistency is killing us but we take our lessons from the game and move on."

There will be those who will argue O'Brien's decision to rest star fullback Kalyn Ponga, key forward Mitch Barnett and winger Hymel Hunt for the game backfired on the Knights.

But O'Brien isn't buying it, believing it was in the best interests of the squad.

"That had nothing to do with the performance," he said. "There are some individuals who are feeling a bit uncomfortable with how they have defended and obviously all that gets reviewed.

"But it's important we put it behind us and move on."

Much of the focus of the review will no doubt be the Knights right-edge defence which leaked the opening three tries of the game inside 16 minutes. Keary was instrumental in all three, laying on the first two for Josh Morris and Daniel Tupou before scoring the third himself.

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After 16 minutes, it was 18-0 and the onslaught continued when Joseph Manu took an inside pass and pushed through some paper-thin Knights defence from close range to stretch the advantage to 24 points.

Newcastle gave themselves a glimmer of hope of a revival when skipper Mitchell Pearce provided the kicks for Edrick Lee to put Enari Tuala over in the corner and Shibasaki to touch down for tries in space of seven minutes to reduce the gap to 24-12. But Roosters fullback James Tedesco's try four minutes from halftime for a 30-12 advantage put the sealer on the match.

Both sides wore black arm bands and a minute's silence was observed prior to the start of the game in memory of the tragic loss of Central Newcastle prop Joel Dark, who died on Friday after collapsing during a game.

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