The Power were completely outclassed by a disciplined Dockers outfit on Saturday night, smashed by 74 points.
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However, Carlton's last-minute loss to Essendon the same night guaranteed the Power a finals berth.
Cornes said the club's mid-season wins over the Sydney Swans and Collingwood proved that at its best, Port was no pushover.
"I think we've shown it throughout the year, our best footy's been really good and we've knocked off some big sides," Cornes said.
"If you said at the start of the year that we'd make finals it'd be a little bit surprising but from round one, first bounce, I think you've been able to see what we can do.
"That achievement shouldn't be underestimated from where we were last year and what we've been able to do this year.
"We need to perform this week, but when we get there the boys will have a lot of belief that they can do some damage."
The 30-year-old has played in 14 finals matches in his 265-game career and said the Power's win over rivals Adelaide in round three gave the side the confidence that it belonged in the top eight.
The Power trailed by 31 points 10 minutes into the third term but overran the Crows to win by nine points.
"The first Showdown showed that 'never give up' spirit and we've been able to produce throughout the majority of the year," he said.
"The boys got a lot of belief out of that."
Before Cornes and his teammates line up for the national anthem in the elimination final though, they must respond from last weekend's heavy loss.
They face a Carlton side on Saturday whose only hope of playing finals now lies in Essendon being stripped of premiership points.
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Cornes said while the loss to Fremantle hadn't shaken the side's confidence, to enter its final on the back of a win was his aim.
"We had a tough one on the weekend and [that] shows you where you sit among the top four sides in the competition … we're pretty keen to bounce back this week against Carlton and put in a much better performance," he said.
"Any heavy defeats we've had we've more taken it as a learning experience … it just shows where we aspire to be – their pressure and how hard they are, they're a seasoned AFL side.
"We'd rather go in with a win rather than a loss, for sure."
Twitter: @AFL_Harry
