The Big Three, from left, Celtics Kevin Garnett, Ray Allen and Paul Pierce joke during a game against the Los Angeles Clippers in February.

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AP / Branimir Kvartuc

You couldn’t ask for a better script.

The Celtics and the Lakers meeting in their first NBA Finals in 21 years, a throwback to the time when the names were Bird and Magic and the NBA was as hot as a Hollywood opening. Back when the Celtics and Lakers were basketball royalty — one of the great rivalries in sports history.

As if this is all direct from Central Casting.

And it only seems fitting.

For if the Celtics are going to get their 17th NBA title, somehow you knew it was going to be against the Lakers, who are right behind them with their 14 championships and their celebrities sitting courtside. Somehow, you knew it was going to have to come against megastar Kobe Bryant and celebrity coach Phil Jackson. Somehow you knew it would come against the showtime that’s always been the Lakers in Los Angeles.

Hasn’t it always seemed to come down to the Celtics and the Lakers, a rivalry that has stretched back to the ’60s, when the Lakers went to L.A. from Minneapolis, and Doris Day — one of America’s celluloid sweethearts — was always in the front row?

Hasn’t it been the Lakers, who throughout that decade were always being billed as the franchise of the future, with their two great young stars, Jerry West and Elgin Baylor, while the Celtics were supposed to be about the past, even as they kept winning NBA titles?

That was the back story, and the intensification of the rivalry in the ’80s just gave it another huge chapter, right there with the “Beat L.A.” chants that used to bounce off the old Garden walls.

They were in the finals three times together then: The lunch-pail Celtics, who played in the drafty old Garden, next to the elevated railroad tracks on Causeway Street, in a neighborhood right out of a grim Edward Hopper painting; the showtime Lakers, who played in something called the Fabulous Forum, complete with the dance team known as the Laker Girls.

All this and Kareem and Pat Riley, too.

That was the story line, and it was heightened by the Bird-Magic rivalry. The best white player and the best black player. The “Hick from French Lick” and the sweet-smiled black kid from Michigan. As if they were as much polar opposites as their teams. As if the Celtics represented basketball the way it used to be and the Lakers represented the way it was going to be.

Simplistic?

No doubt.

But when did that ever get in the way of a great story?

Now so much is changed. The NBA is all showtime, the Garden in Boston no different from the Staples Center in L.A. It’s all the same, the pyrotechnics, the same energy, basketball game as carnival.

And truth be told, there’s not a whole lot of difference between the two teams either, just a matter of degree. A year ago, the Lakers went out of the playoffs in the first round, and Kobe Bryant spent the entire off-season saying he wanted to be traded. He said he was tired of the team’s mediocrity.

But in early February, the Lakers traded for center Pau Gasol, and here they are in the finals.

“A dream come true,” Bryant said the other day. “An answer to a prayer.”

We all know about the Celtics.

We all know that a year ago they limped through a 24-win season, their glory days seemingly as far behind them as Johnny Most and Red Auerbach. We all know how they acquired veteran shooter Ray Allen on a draft-night trade, and then the great Kevin Garnett in another huge trade. We know that those two joined Paul Pierce in the new version of the Celtic Big Three and how they became the cornerstone of the best turnaround in NBA history.

Could you ask for a better script?

“There’s nothing better than this,” Pierce said after Friday night’s win against Detroit.

“This is what I came here for,” echoed Garnett.

Those were not just empty words.

Each one of the new Big Three knew they were going to have to subordinate themselves if this were going to work; each was going to pay a price if the Celtics were going to evolve into a real team, or else just be a collection of guys all dribbling to their own beat.

“It started from day one,” Pierce said. “We knew we had to sacrifice our scoring.”

So they talked Friday night about how they all had to commit themselves defensively, had to commit themselves to being leaders. For all their individual successes, none has ever won an NBA championship.

Now they are in the finals, four wins away from a sliver of basketball immortality. Four wins away from bringing a 17th world title to Boston and another banner to hang forever in the rafters.

Their first shots will be on Thursday and Sunday nights, in Boston, at the TD Banknorth Garden.

“We don’t want the silver ball,” said coach Doc Rivers. “We want the gold ball. That’s what we’re playing for.”

And as fate would have it, that’s going to take beating the Lakers, their age-old opponent.

As if after all the years and all the players it all comes down again to these two teams, these two basketball alter egos. As if you close your eyes and the names could be Baylor and West versus Havlicek and Russell, Bird versus Magic, the names changing but the tradition rolling on, right there with the “Beat L.A.” chants.

A new chapter in the rivalry for a new generation.

Direct from Central Casting.

breynold@projo.com