NBA

Knicks should enjoy potential closeout game, but can’t lose their heads

Nobody is saying the Knicks have to treat tonight’s Close-Out Game No. 2 like High Mass, a solemn occasion to which laughter is not invited. Nobody is suggesting this has to be a grim, joyless evening of reflection.

On the contrary: Madison Square Garden ought to be a rollicking funhouse tonight, because if the Knicks take care of business it’ll be the first time they’ll win a clinching playoff game at home since June 11, 1999 against the Pacers, Game 6 of the Eastern Conference Finals. Fourteen years is plenty long enough.

So, yes: if J.R. Smith wants to go the slapstick rout with regards to Jason Terry — “Who’s that?” he asked, keeping a quasi-straight face yesterday, “I don’t even know who that is” — there’s technically nothing wrong with that. If they want to celebrate during games — “showboating” being the word of choice for the Celtics — well, that’s fine too, especially since it isn’t as if the most prominent Celtics are ever terribly bashful about enjoying themselves when times are good.

Still …

You’d like to believe there were some lessons learned across the past few days, starting with the moment Smith’s elbow collided with Terry’s chin, proceeding through the lost opportunity of Sunday when, even without Smith’s usual contribution of 18 or so points, the Knicks found themselves up a deuce in the final minute and couldn’t shut the door.

You’d like to think the days when the Knicks as an organization celebrated small victories — like dropping balloons and confetti after a single playoff win against Miami last year, grateful for simply staving off a sweep — are done, and that the mission would register down the corporate flow chart to the floor.

Put it this way: You didn’t see the Celtics offer up any pyrotechnics after buying themselves three more days of season Sunday afternoon at the TD Garden, and while there are plenty of things a Knicks fan can dislike about the way the C’s do business, this core has been awfully good about taking care of the bottom line since it was put together in 2006. The Celtics generally close when given the opportunity to close.

And don’t let petty nonsense get in the way.

Add that to the lesson plan awaiting the Knicks tonight.

“There’s big-time urgency on our part,” Knicks coach Mike Woodson said yesterday after running the Knicks through what he hopes will be the final practice session of the first round. “We played the whole season for this, to be able to close a series out in front of our fans. I’m expecting our guys to step up and play.”

For Woodson, though, there is still an element of the unknown at play here. There are pieces of the Knicks’ puzzle who act like they’ve been there before because they have actually been there before. Jason Kidd and Tyson Chandler won a championship two years ago in Dallas. Kidd and Kenyon Martin went to back-to-back Finals with the Jersey Nets a decade ago.

But most of this team own playoff resumes that are checkered at best, and this group as a whole has yet to do anything together besides win a division championship. A lot of what they’re doing in these playoffs is being done on spec. Carmelo Anthony, famously, has but two playoff series wins. Same with Smith. Ray Felton never has won one. Neither has Steve Novak.

“This is a new group,” Woodson said. “And what they’re learning is that in playoff basketball, anything is liable to happen. We have to save our energy and stay composed on the floor. If we play the way we’re capable of, we’ll be all right.”

There is a key element there, of course: if.

The Knicks are done getting their feet wet in the playoffs, done chasing the butterflies. This is about business now, about securing their place in the second round and then hoping the Pacers-Hawks series isn’t decided, one way or another, until the fifth overtime of

Game 7. It’s about assertion and will and sending a message to themselves they can handle prosperity.

That means acting like they’ve been there before, even those who haven’t been there before, if they win tonight. It means walking away from frustrated Celtics with nothing to lose if they’re itching to start something, the way some around the Knicks believe Terry goaded Smith the

other night. They can have fun tonight; hell, a night like tonight is

supposed to be fun if all goes as it should.

Celebrating serendipity is fine.

It’s stupidity they have to be on guard against.

michael.vaccaro@nypost.com