BOSTON – They’re going to do right by him tonight. Not all of them, maybe. There is a segment of sports fan that will cut you off the moment you change uniforms, no matter the circumstance, no matter the reason, no matter the city.

These are the Giants fans who hooted Sam Huff, the Knicks fans who threw out their Patrick Ewing jerseys, the Mets fans who will stay seated on Aug. 8 when Mike Piazza returns to Shea Stadium as a Padre.

They are a distinct minority. And they will be outnumbered tonight at Fenway Park, when Pedro Martinez walks to the mound in the bottom of the first inning.

Most of the Red Sox fans in the house, they’ll do the right thing. They’ll cheer Pedro when he makes the long walk from the third-base dugout to the outfield warning track for his pregame long tosses. They’ll cheer him when he takes his warm-up throws in the bullpen.

They’ll cheer when his name is introduced as part of the starting line-up, when his picture is plastered on the video board. They’ll cheer when he walks back from the bullpen to the dugout.

And they will positively lose their minds when he walks to the mound.

They’ll stand. They’ll clap, and stomp their feet, and they’ll chant “Thank you, Pedro!” and they won’t stop until he tips his cap once, twice, three times.

And then they’ll root for the Sox to pound the hell out of him.

“If they clap for me, I’ll be really happy,” Martinez said yesterday, a few hours before the Mets and the Red Sox met for the first game of a fascinating three-game showdown between the two best teams on the Eastern seaboard. “But if they don’t, I’ll just have to say they’re doing it to back up their team, which is the Red Sox, not the Mets.” He won’t have to worry about that, not if the early indicators are true.

Not if the electric buzz circulating through the city’s streets yesterday is any indication.

In the saloons, in the restaurants, in the hotel lobbies, the people talked about Pedro, the same as they did when he played here, and mostly they spoke of him fondly.

Martinez himself said that when he walked around town the last few days, “it felt like the old days. People talking, saying the same things they used to say.” They know. They have to know. It’s something Mets fans can relate to completely, because the same thing Pedro has become to this formerly forlorn team is precisely what he was to the Red Sox. It wasn’t just that he turned the Sox from pedestrian to powerful just by showing up, although that’s what he did, and that’s what he’s done with the Mets.

It was more than that here, and it’s more than that with the Mets. Shea Stadium is more than just a ballpark now on the days he pitches, it’s a place filled with possibility, overflowing with energy, the people flocking there because they know with him on the mound, they might well see something they’ve never seen before. It’s an event. A happening. A festival.

“When I came to Boston, Fenway Park was all about applauding when things were good and booing when they were bad, and that was it,” Pedro said with a smile. “There was no singing, no dancing, no laughing. I think we showed Red Sox fans how to have a really good time at Fenway Park.” And in their spare time, they ended an 86-year championship drought, too.

All of those things will be inside the old ball yard tonight, all those old memories, all those old passions, all those old emotions.

That alone should be enough to get the Sox fans on their feet.

Some won’t budge. Some will hold a grudge. Some will ignore the fact that the Red Sox could have matched Pedro’s deal at any time, and that it can be argued that the team may have owed him that much for helping to transform the Sox into the ATM machine they’ve become. Some will always boo the uniform.

Most of them won’t. They’ll do right by him. As well they should.