The notion of a "trap game" practically is as old as the NFL itself, but that doesn't make it any less legitimate a danger for the Giants this week.

Coming off a huge, emotional road win in Philadelphia over a bitter division rival that had beaten them six previous times, the Giants now must travel across the country to take on the 1-2 Cardinals — a mostly anonymous franchise that somehow lost to quarterback Tarvaris Jackson and the Seahawks last week.

If that doesn't create the prospect of a big letdown by Big Blue, it's hard to imagine what would.

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"The team we played last week was definitely a good football team," Brandon Jacobs said yesterday of Sunday's 29-16 upset of the Eagles. "We knew everything that they did, and they know everything that we do. It's a divisional game. We play them twice a year. We're not too familiar with what [Arizona] does."

Wide receiver Larry Fitzgerald, defensive tackle Darnell Dockett and safety Adrian Wilson are big names, and former Eagles quarterback Kevin Kolb is no mystery to the Giants. But after the Cardinals were sent to the NFC West as part of realignment in 2002 after decades alongside the Giants in the East, Arizona has been mostly a case of "out of sight, out of mind" for Tom Coughlin's team.

The teams have played just five times since realignment, with the Cardinals winning the most recent matchup at the Meadowlands in 2009. Eli Manning's only start at University of Phoenix Stadium — not counting the Super Bowl — was three years ago, when he threw three touchdown passes in a 37-29 win.

Justin Tuck, who might not play Sunday because of lingering neck and groin issues, admitted last week's game was unusually emotional because of the losing streak to Philly in general, and the horrific fourth-quarter collapse against the Eagles last December in particular.

The Giants finished the job this time, and Tuck, the defensive captain, said the memory of that can energize them this week, too.

"Everybody that was here last year knows about getting overconfident, about what can happen if you only play 31⁄2 quarters," Tuck said. "There's enough [veteran] leadership on this team to let everybody know that we've got a long way to go."

And it's not as if the Cardinals are pushovers. Running back Beanie Wells, who has been dealingwith a hamstring injury, appears likely to play Sunday and is tied for third in the NFC in rushing while averaging 5.7 yards per carry, Kolb is completing 63 percent of his passes and Fitzgerald is a perennial Pro Bowl selection.

But except for ex-Cardinals safety Antrel Rolle, who is friends with Dockett and would love nothing better than to beat his old team, the motivation to beat Arizona for any reason other than to improve their record to 3-1 isn't really there for the Giants.

A letdown appears to be a concern for Coughlin, who said yesterday he stressed to his team the importance of forgetting the win over the Eagles as quickly as possible and letting it be "a springboard to the future and not reflective of the past."

"Last Sunday was over, as far as I was concerned, on Monday," Coughlin said. "We're moving on. We have to move on. I think our team realizes that, and hopefully we can use it as a real plus to help us go forward."

Tuck, however, doesn't want the Giants to eject last week's win from their memory banks entirely — at least not yet. He would like for the message that his team can overcome a flood of injuries and still represent itself proudly to linger for a while.

"That game against the Eagles proved we have talent," Tuck said. "It proved to a lot of people around the country that we could lose people and still play with anybody in this league."

The Giants just need to prove that all over again Sunday.

bhubbuch@nypost.com