BOSTON — Ray Allen moved to Miami over the summer, and that’s not the only reason that Boston Celtics coach Doc Rivers is focusing his attention on LeBron James and Co.

The biggest hurdle for the Celtics on the way to another NBA title is now within their conference — the first time since the New Big Three was assembled that Boston has had to worry about a reigning champ within the East.

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Rajon Rondo, right, and the Boston Celtics take on the defending champion Miami Heat in their season opener Tuesday night. ASSOCIATED PRESS

“I honestly rarely look at the West,” Rivers said at media day after discussing the moves the archrival Los Angeles Lakers made over the summer. “I could care less about the West, because at the end of the day we have to get out of the East, and the defending champions are in the East.

“So, we have one target, and that’s Miami,” he said. “Whatever happens out West: Good luck. Hope to see you. That’s how we think about it.”

Allen’s departure broke up the trio that brought Boston an unprecedented 17th title in 2008 — its first since the original Big Three of Larry Bird, Kevin McHale and Robert Parish won it all three times in the 1980s. But Allen had been relegated to bench duty anyway, with Rajon Rondo filling his role as an All-Star alongside Kevin Garnett and Paul Pierce.

Now comes the Big Three, 3.0.

The Celtics insist that this is Rondo’s team now, acknowledging a fact that has been apparent for some time as the young point guard has taken over on the floor. Last season, he had a career-high 11.7 assists per game along with six triple-doubles in the regular season and four more in the playoffs.

Jason Terry — fourth on the NBA’s career 3-pointer list — is a logical replacement for Allen, who took less money to join the defending champions, perhaps because of a rift with Rondo. Courtney Lee will also help out at guard — at least until Avery Bradley, who pushed Allen out of the starting lineup, returns from shoulder surgery that is expected to keep him out until December or January.

But the most encouraging sign for the Celtics is the youth infusion that could help bring energy to a team that has been dominated by Garnett, now 36, and Pierce, 35.

“We’ve got a lot of guys who have been in the league a long time, a lot of dinosaurs,” said Jared Sullinger, one of two first-round draft picks. “When you see guys who have been in the league for 10 years, in some cases 17 or 18 years, … (they’ve) seen it all. So if you listen to them, they are only trying to help you.”

Garnett praised Sullinger’s basketball intelligence and willingness to learn.

“I’m giving him the book,” Garnett said, “teaching him everything I know.”

Jeff Green is back after heart surgery and demonstrating — in the exhibition season, at least — some of the talent that prompted the Celtics to break up their 2008 championship team by trading Kendrick Perkins to Oklahoma City.

Boston also has two first-round draft picks ready to contribute.

Sullinger, who led Ohio State to the Final Four last season, was once a potential lottery pick before questions about his health dropped him all the way to 21st overall. Center Fab Melo was taken with the next pick, and his Syracuse teammate Kris Joseph came to Boston in the second round.

“I think there’s a lot of growth in our team,” Rivers said. “How fast we do it, who knows? We’ll figure that out as the season goes along. But if we do grow in all the different ways we can play, everyone kind of gets it, I think we can be very, very good.”

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