MIAMI - Chris Bosh had been preparing for this moment all season. He had been hoisting threes in practice, an unusual task for a big man, waiting for his moment. He knew that at some point he would be called upon to use this skill to perhaps win a game.

It all happened Saturday night.

“I know it will surprise a lot of other people, but I’ve been practicing those things all year,’’ Bosh said. “We’ve been getting a lot of shots up all year. We kind of knew in big-time situations that they were going to be open, and I would be able to shoot it without hesitation.’’

He was open and on target. He made the shots, three 3-pointers, all of them crucial, in the Heat’s 101-88 win over the Celtics in Game 7 of the Eastern Conference finals.

Bosh had proclaimed himself 99.1 percent ready Saturday afternoon, a tick better than he had been Thursday. But that’s not the way he played. He played as if his health had never been an issue, as if he were born to hit 3-pointers, as if he wanted to take on the role of the biggest of Miami’s Big Three.

And, after the game, he proclaimed himself at 99.2 percent.

“We all had a pit - even though we didn’t admit it - we all had a big pit in our stomach when we saw him walking off the court in Game 1 of the Indiana series,’’ coach Erik Spoelstra said. “We all shuddered at the thought. We played tough, but we knew that for two years he had been our most important player, because he makes it all work.’’

Through the rest of the Pacers series and the first four games against the Celtics, the Heat struggled at times to fit the pieces together without Bosh. They were adjusting on the fly without a critical piece.

When he returned, it all went back to normal.

That made Bosh the difference in Game 7 - and perhaps in the series. Had he not returned, it’s possible the Celtics would be heading off to Oklahoma City. But he did, and the Celtics were bound for Boston and the offseason.

“He showed up big,’’ Spoelstra said. “It’s a testament not only to his talent, but his character to be able to keep on working, grinding, allow us to work him back and integrate him slowly coming off the bench. No issues at all ever.’’

Despite not starting, Bosh played 31 minutes, and had 19 crucial points - including those surprising three 3-pointers after hitting just 10 this season.

He had returned in Game 5, managed just 14 minutes. He played 28 in Game 6, asking out of the game twice because of the abdominal injury. He needed little rest in Game 7, and did everything the Heat required of him. He added eight rebounds and was 8-of-10 shooting.

Nine of his points came in the first half, during which both Dwyane Wade and LeBron James were not playing up to their capabilities or reputation. Bosh, on the other hand, was.

“Chris was big,’’ James said. “Huge,’’ Wade concurred.

“Game ball automatically goes to [Bosh],’’ James said. “To come off the bench for 19 and eight is huge. We haven’t had that kind of fire power off the bench.’’

It was Bosh’s first Game 7, the only one of Miami’s key trio never to have played in one. And he distinguished himself, treating the game like any other, as he said before the game.

Even though Bosh sometimes gets ignored amid the star power of Wade and James, that was hardly the case on this night. In some ways, he eclipsed both.

He was what they needed, when they needed it.

Bosh had thought about playing in a Game 7 for a long time. Moments that he knew he could conquer.

“Ever since I played Little League, I remember playing championship games in my backyard with my 10-and-under teams,’’ he said. “That’s when it started for me. And I think about those moments all the time.’’

He made the shots when he needed and helped lead his team over the Celtics.

“Sometimes I fail, but most of the times I succeeded,’’ Bosh said, of those backyard games. “And that helped me believe in myself. It helped me believe in the situation and my teammates as well. And it gave me the supreme confidence that I needed coming into this game.

“When you play like you don’t know there’s a tomorrow, you can play free. That’s what I did tonight.’’