Young North Melbourne defender Lachie Hansen is relishing the challenge of taking on the AFL's best power forwards.

With more experienced defenders Michael Firrito and Josh Gibson shifted upfield to bolster the Kangaroos' midfield, the tall, athletic 20-year-old has been earmarked as the key man in the club's defence.

It is a major step up, having spent his 13 games in his previous two seasons playing mainly on the opposition's third best tall forward.

But having added 5kg to his frame over the pre-season, he started his new role in fine style last weekend, keeping Melbourne's Brad Miller goalless.

His next task will probably be to rein in bullocking Western Bulldogs forward Mitch Hahn at the MCG on Sunday, after Hahn booted five goals against Fremantle in the opening round.

Hansen said it took a notable step up in concentration and endurance to man the opposition's key targets.

"They'll kick it to them a lot more, so their workrate is greater, Miller was hitting up all the time, you've always got to be up their arse," Hansen said.

"When you're on the third tall, they normally don't get used as much so it's a bit more cruisy.

"But when you're playing on the key forwards they get used a lot so you've got to be on your game. It's good, I like the challenge."

Provided he holds his form, Hansen is looking forward to taking on a roll-call of the AFL's star forwards, such as Jonathan Brown, Matthew Pavlich and Barry Hall, during the season.

"I wouldn't mind getting a crack at all those guys this year," he said.

"It's my third year, I'm feeling really confident out there."

Fellow youngster Scott Thompson has also been earmarked for a regular key defensive post.

Hansen acknowledges the pair are under pressure to perform, given Firrito and Gibson could otherwise have to step in, causing a flow-on effect in the midfield.

Experienced backman Daniel Pratt said it was exciting to see the club's younger players stepping into bigger roles.

"It just takes a little bit of strain off blokes like Firrito and Gibson who are generally fighting out of their weight when they play," Pratt said.

"Scotty Thompson's the strongest bloke at the club and Lachie's not far behind, so it's good having a couple of taller defenders playing back there."

Pratt is preparing for his own tough defensive assignment on Sunday, against Bulldogs skipper Brad Johnson.

"I've played on him most other times, so I look forward to playing on him and we've had a few good battles," Pratt said.

North have won their past five games against the Bulldogs.

But the 'Dogs were impressive in their opening round thrashing of Fremantle and Pratt is expecting the new-look 'Roos side to be pushed harder than they were against Melbourne.

"It was good just to get the win on the board, but this week will be the real tester I think."

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