Port Adelaide coach Mark Williams says the Power are "desperately disappointed" to have blown the chance to skip clear of the logjam on the AFL ladder.

Port's five-point defeat to North Melbourne at Etihad Stadium on Saturday night cost them the chance to secure outright third spot.

Instead the 20.5 (125) to 18.12 (120) defeat, which included a charge that came too late, has them at 4-3, still encouraging, but now just one of 11 sides separated by one game and chasing the unbeaten St Kilda and Geelong.

For a side capable of beating reigning premiers Hawthorn and outclassing hometown rivals Adelaide last week, Port's defeat to the lowly Kangaroos was inexplicable.

Williams said his side was beaten in "all the hard stuff" early, and that the result confirmed the Power were a middle-of-the-road side.

"We're desperately disappointed with how we played," he said.

"Last week we won and I said we're just a battling side and this week we lost and I still say the same thing.

"... it's a fine line in footy.

"We're very understanding that the pack is there.

"Fremantle won (last) night and they started poorly and have come good, Brisbane have won at the MCG.

"There's going to be lots of different results and surprises this year because the competition is so close."

Port's pursuit of redemption in the round eight game against struggling Richmond will be hampered by a couple of serious injury concerns.

Key onballer Kane Cornes hurt his AC joint in a bump from Roos veteran Adam Simpson, and the Power are not sure how serious the injury is.

Simpson was reported for the contact.

Steven Salopek also suffered a shoulder injury, a dislocation, and could be sidelined for a month.

Williams at least took heart from Port's comeback, when they booted four goals inside five minutes to nearly pinch the game.

The fightback was encouraging given Port did not offer a yelp in their two other defeats this season, to West Coast and the Saints.

"We'd much rather fight back than not, that's a quality we'd like to think that we've got inside us and it was good to see that a lot of the young blokes that led that, and that was great," Williams said.

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