Boston ? This is not how the Boston Celtics planned to get back to the NBA finals.

The league’s luckiest franchise saw its luck run out – again – in the draft lottery last year, coming up with the worst possible pick and no shot at the megastars slotted 1-2. What the Celtics couldn’t know at the time was that it was the best thing that could have happened.

“We hit rock bottom with the lottery – as bad as we could do – and then Danny (Ainge) went to work,” co-owner Bob Epstein said Sunday. “Not everything is a master plan. A lot of skill in any endeavor is being able to be opportunistic as well.”

The Celtics took advantage of their opportunities just fine after the lottery setback, landing Kevin Garnett and Ray Allen in trades that helped them reach the NBA finals for the first time since Ainge and the original Big Three made it there in 1987.

Game 1 against the Lakers will be Thursday night.

In a series of interviews over the weekend, the owners who bought the team in 2002 explained the turnaround from 24-58 lottery loser to Eastern Conference champion. It didn’t happen that night at the draft lottery, and it didn’t even happen during the monthlong trading spree in which Ainge brought in Garnett and Allen to join with All-Star holdover Paul Pierce.

“Everybody wants to talk about the overnight success, but I think that this was five years in the making,” co-owner Steve Pagliuca said. “The plan was: draft well, build up chips and build this into a championship team. We had the pieces, and we thought something good was going to happen – this year, next year. It came together very nicely.”

The NBA’s most decorated franchise, the Celtics were once synonymous with success – winning 16 championships from 1957 to ’86. But twice since their last title they’ve dropped to the bottom of the standings in hopes of landing a big lottery prize, only to see the chances go against them.

With two potential franchise players at the top of last year’s draft, Greg Oden and Kevin Durant, the Celtics seemed in good position to pick up a key part of their turnaround. But three teams jumped over them in the lottery, and they wound up with the No. 5 selection.

“It was the worst possible pick we could have gotten, and it felt like the worst possible thing,” said managing partner Wyc Grousbeck, who was in the sealed-off room where the lots were drawn and found out about an hour before the TV audience that the Celtics had dropped to the fifth spot.

“I spent 50-55 minutes going, ‘This is really terrible. I feel really badly for all the Boston fans who were about to find out.’ I just felt really unlucky,” he said. “There was no joy in Mudville.”

Then came Plan B. And C.

Ainge tried to trade the No. 5 pick and developing big man Al Jefferson for Garnett, but Garnett didn’t want to come to a losing team, and the Celtics didn’t want him unless he’d agree to an extension. So Ainge sent the first-round pick – which, other than Paul Pierce, was his most valuable commodity – to Seattle in a package for Allen.

Suddenly, Garnett was interested. Ainge picked him up from the Timberwolves in an unprecedented 7-for-1 deal, and the Celtics were on their way to 66 wins – the biggest turnaround in NBA history – and a return to the finals against their archrival.