Damon Harrison is one of the Giants who will be playing his first playoff game Sunday, so he’s relying on the handful of teammates who have some experience in the postseason.

“We’ve had some guys talk to us who have been there before, letting us know how it’s gonna be with the atmosphere,” the ex-Jet said following practice Thursday, as the Giants finalize preparations for Sunday’s wild-card game in Green Bay.

Their message, from players such as Eli Manning, Victor Cruz, Jonathan Casillas and Zak DeOssie, is simple, according to Harrison.

“Just being focused and not trying to change up too much,” Harrison said. “Just do what you did that got you to this situation. If you’ve been a consistent guy, just remain consistent. Stay true to your technique. In this situation, guys try to stretch and make plays and end up messing up.”

There’s been little of that — especially on defense — for the Giants as they finally broke their own playoff drought.

And a big part of the defense’s effectiveness has been the line, which includes not just the newcomer Harrison, but another playoff neophyte, Olivier Vernon.

Both were brought in last offseason in the Giants’ free-agent splash that also included Janoris Jenkins and has quickly paid dividends.

“I wouldn’t say there are any butterflies,” said Vernon, who spent four years with the Dolphins before arriving to MetLife Stadium. “A lot of guys are excited to have the opportunity. You don’t get too many chances to be in the postseason. … It’s gonna be a hostile environment. I can’t wait to get there.”

If they want to last more than one week, they’ll have to somehow limit Aaron Rodgers — but that won’t be easy.

“Most definitely you need to get to him — as well as be disciplined,” Vernon said. “Just getting in his face is the biggest thing. Put pressure on him. We’ll see on Sunday.”

Vernon had 8.5 sacks this season and Harrison, signed primarily to be a run-stopper, has become a more significant factor on the pass rush in recent weeks.

“At this point in the season — or postseason — guys are willing to do anything,” Vernon said. “[Harrison] is out there with us not only on the rush, but on pass because it’s all hands on deck.”

For the most part in recent weeks, it’s worked.

Asked what the secret was, Vernon said, “I don’t know. Just playing good Giants football. That’s it.”

Whether that is enough to stop Rodgers and the Packers’ potent offense remains to be seen — and the Giants who haven’t been to the playoffs will have to learn fast.

“It’s the opportunity of a lifetime,” running back Rashad Jennings said. “They say, ‘Act like you’ve been there before.’ Guess what? I ain’t never been there, so I don’t know how I’m gonna act.”

But fear not, Giants fans. Harrison insisted something in his background could come in handy come Sunday.

“I have a lot of experience in the playoffs,” Harrison said. “I just won the Super Bowl on Madden. I go to the playoffs every year.”

On Sunday, though, he’ll have to face Rodgers & Co. for real.