BOSTON — It has become the NBA version of sacred ground.

Home court.

Defend it, or it will come back to haunt you.

Defend it, or it will exact its pound of flesh.

Last night, the Celtics defended it, using the same old script they’ve been using since these playoffs started, the one that got them past both Atlanta and Cleveland. Let the devil take tomorrow. Just win at home.

And they did it in the fifth game, the most important game of a series. Did it in a game in which Kendrick Perkins had the first half of his life with 12 points and 13 rebounds, a great performance that kept the Celtics in a game when they were down eight with eight minutes and change left in the second quarter, a game that seemed to be being played direct from the Detroit playbook.

That was the highlight of a first half when the Celtics absolutely killed the Pistons on the glass, a 28-11 rebound advantage at the half, and a six-point lead at the half.

That set the tone.

After that, the Celtics seemed to ride the tide, fueled by the crowd and the energy that ran through the building like some kind of electric current, the energy the Celtics have rode through these playoffs like some magic carpet. Throw in a vintage Ray Allen performance, some retribution for what’s been a tough playoffs for him, and the Celtics put their imprint all over this game in the third quarter, and it seemed all over but the shouting.

Not quite.

But take away Game Two when the Pistons grabbed a game here in the Garden. One of the stories of these playoffs is how tough the Celtics are to beat at home, how difficult it is for a team to come in here and win. Last night was simply more of the same, even if it seemed for a while that the Celtics were going to let this get away.

They did not.

And when it was finally over, after three hours and 45 minutes of playoff basketball, there was really little mystery to it.

This is now all about defending the home court for the Celtics, the reward they got for the regular season, all those games in a season in which it seems that there are a zillion of them, all those games that often go by all but unnoticed. That all came into play last night, another night in the Garden that seemed like old times, back when big games in the playoffs seemed as if they were simply part of the schedule.

That was the game plan last night, and after the Celtics shook off a good start by the Pistons, this team that’s won so many big games before, it was what we’ve come to expect from this team in the Garden.

“We’re going to be who we are, and they’re going to be the same, and we’re going to go out and play,” Doc Rivers had said before the game.

So much for pretense.

There are few surprises in the fifth game of a series. Everyone knows everybody. All the tape has been watched. There are few mysteries left.

We know the Pistons are a tough, veteran team that knows how to win big games. We know they’ve already proven they can win a playoff game in the basketball hothouse that’s Boston’s TD Banknorth Garden. We know that halfcourt, grind-it-out games seem to favor the Pistons. We know that few things come easy against the Pistons, this team that’s in its sixth straight Eastern Conference final for a reason.

We also know that the Celtics went into this series winless on the road in the playoffs, unable to win in either Atlanta or Cleveland, even if they had had the best road record in the NBA in the regular season. The fact they had to go seven games in both those series, and the very real possibility that if they didn’t have the home-court advantage their season already would be over.

Thank the hoop gods for the home court.

So it went last night.

For we knew the Pistons were going to make a run in the fourth quarter, knew they weren’t going to go quietly in a fifth game. Knew they were going to battle the crowd and the noise all the rest of it and make a charge. We just didn’t know it was going to be quite so dramatic.

But it was just a one-point game with just about a minute left, the Celtics falling apart and the Pistons about to come back from 17 down in the third quarter and make a miracle comeback, when Allen buried a jumper from the left corner. The same Ray Allen who has been much maligned through so much of these playoffs.

The Celtics had escaped.

Once, again, it was the same script in these playoffs this NBA version of defending sacred ground.

Defend the home court, or it will come back to haunt you.

Defend the home court, or it will exact its pound of flesh.

Last night the Celtics did.

Barely.

breynold@projo.com