YOUNG Carlton big man Lachie Henderson always shaped as a key figure in Friday night's clash with North Melbourne.

Known largely as a forward during his short AFL career, the 21-year-old had been thrown into defence in the past month as cover for injured full-back Michael Jamison.

On Friday night, the inexperienced defender faced his toughest test yet against in-form Kangaroos forward Drew Petrie.

Pass, and the Blues were near certain to prevail. Fail, and an upset was on the cards.

That his team eventually won by 18 points gives a strong indicator as to Henderson's contribution.

The former Brisbane Lion, who arrived at Carlton as part of the trade deal that sent Brendan Fevola north, held the dangerous Petrie to just five marks and two goals, ranking him easily among the Blues' best performers.

Coach Brett Ratten had no doubt as to Henderson's impact on the result.

"Let's talk about Petrie's form in the last six or seven weeks; it's been outstanding," Ratten said.

"So he (Henderson) played on a very good player and won that battle."

Expectations on the No.8 pick in the 2007 NAB AFL Draft have been high ever since his arrival at Visy Park at the beginning of 2010.

Last year he showed definite promise with 25 goals from 19 senior appearances, but just when a big 2011 seemed certain, hip surgery stalled his preparation for the new season.

"He's just building with his own confidence," Ratten said.

"It's a hard thing when you miss 13 weeks of pre-season after Christmas, and he's just taken a bit of time and momentum.

"But I thought his work tonight was probably one of his best games for our footy club."

With Jamison set to return from his knee injury in the coming weeks, Henderson's success as a backman means Ratten will have flexibility.

He can shift the youngster forward into attack, or leave him to work as a second key defender.

Most likely it'll be a little bit of both.

"It'll come down to list management at the end of the season and who's suited where and things like that," Ratten said.

"But it gives us a real shot of confidence in his ability to play on good players back there and do the job.

"'Jamo' is going to play at full-back, but even in good form there'll be games when he gets beaten.

"So we need to have a plan B, and Lachie's going extremely well."