The Roos' only game outside of Melbourne before round 12 is a clash with Geelong at Skilled Stadium and Petrie admits there is some urgency to beat Essendon at Docklands on Sunday.
Victory over Melbourne in round one was followed by losses to the Western Bulldogs and Hawthorn, however, North's next four games – with the balance of opponents including Richmond, Collingwood and Port Adelaide – are all very winnable.
"We need to make inroads now," Petrie said. "We haven't so far and the next seven games will be important and will shape our season.
"The back half of the year sees us travelling every second week. It's hard to win interstate but we've done that in previous years."
A quirk of the fixture means that apart from a NAB Challenge match in Bendigo, North hasn't played Essendon since round one, 2008.
The Bombers won that encounter by 55 points but only added seven more victories for the season and finished 12th.
After losing to Port Adelaide to open 2009, they've beaten Fremantle and Carlton – which looked like this year's big improver.
"I watched the game on Saturday night and they were quite impressive," Petrie said of Essendon. "Their side's full of youngsters at the minute.
"It's dangerous playing against sides with youth because they get excited and certainly that reflects in the way that (veteran full-forward) Matthew Lloyd played. No doubt he was that excited about what was going on up the ground that it helped him perform the way he did.
"It's an unknown quantity a little bit too with so many youngsters in their team. You certainly have to do your research on the guys who you don't know much about."
Petrie said his teammates would make a point of avoiding the free kicks and 50m penalties they gave away against Hawthorn last weekend, with Petrie's grapple of Lance Franklin gifting the forward his second goal.
Moments of frustration also saw a number of North players arguing with umpires.
"Certainly something we haven't been this year [before last week] is undisciplined," Petrie said. "You certainly can't afford to be giving up 50-metre [penalties] every quarter to sides and allow them easy shots on goal. We'll fix it up this week.
"Possibly individuals' games weren't going to plan and you do tend to get frustrated. That's when you can become undisciplined.
"I guess that was just a sign that Hawthorn were on top of us and were playing really well."
Petrie added that coach Dean Laidley hadn't raised the players' discipline in his match review.
"The week's not over yet so I'll still wait to hear from him," he said.
