NATHAN Buckley didn't like what he saw in the final 45 minutes of Saturday night's win over Gold Coast, saying Collingwood played some of its worst football of the season.

And things might get a further complication with reliable defender Lynden Dunn suffering a knee injury that is "concerning" to his coach.

The Magpies vaulted to second on the ladder with their 39-point win, but after playing scintillating footy for the first two-and-a-half quarters, failed to go on with it.

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Buckley's men led by 59 points midway through the third term, before dropping their work-rate and their skill level to let the plucky Suns close the gap.

Gold Coast got within 32 points and butchered some easy chances to narrow the gap even further.

"I thought we played as good a footy in the first two-and-a-half quarters as we've played," Buckley said.

"I really thought it was a challenging contest.

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"Then we dropped right off. It looked like physically we weren't able to maintain it.

"It was an ugly game of footy for the last 45 minutes.

"We played some of our best footy and we played some of our worst.

"We'll take the win. We never take anything for granted."

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Things were not helped by Dunn's injury late in the third quarter, when the veteran landed awkwardly in a marking contest with Nick Holman.

Buckley said it was a "jarred knee" that would need further investigation, but he was concerned.

"We think there's some damage in there," he said. "We don't know what it is.

"We'll scan in the next couple of days and see what he's got.

"It's concerning. You don't like players that don't finish the game off."

One thing that typified Buckley's annoyance in Collingwood's win was its lack of rotations in the third quarter, which the coach said cost his team.

"We had a period in the third quarter where we didn't rotate anyone for 20 minutes. I think that bites you," he said.

"The work-rate of our players dropped off. Gold Coast looked like they were able to maintain theirs.

"We didn't like what we saw.

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"When you're going well, sometimes players don't want to come off, they're enjoying themselves that much they want to stay out there, but the discipline to do that, it's an under-rated part of it.

"You do need to share the load physically, you've got 22 players.

"When you do miss out on a couple of rotations, it does affect you.

"When you've got 18 blokes that decide not to rotate for a period of time, or the play gets stuck (on one side) … it'll come up in our review and see if it's got any merit.

"We're clutching at straws because it went from really good for us to not great."