PORTLAND – The Boston Celtics have always been the Maine Red Claws’ first choice as an NBA affiliate. Now they’re the only choice.

The Celtics and Red Claws announced Thursday that they have entered into a single-affiliation agreement beginning with the 2012-13 NBA Development League season.

In their first three seasons, the Red Claws were affiliated with the Celtics, the Charlotte Bobcats and the Philadelphia 76ers.

Under the new three-year agreement, the Celtics will have full control over the Red Claws’ basketball operations, including hiring a head coach, filling the roster and paying all basketball-related expenses. The cost is around $220,000 per year, say team officials.

While the Celtics didn’t send any players to Portland last season — Celtics President Danny Ainge said injuries that depleted the NBA roster and the labor dispute that shortened the season prevented it — the new agreement will make player movement easier for both clubs.

The Red Claws will remain under their Portland-based ownership group, which will continue to run all business aspects of the organization.

“In our three years we have had outstanding support from our fans,” said Bill Ryan Jr., chairman and president of the Red Claws. “And a huge part of that support stems from our relationship with the Boston Celtics. Obviously, Maine is a huge Celtics stronghold and it’s always been extremely important to us to have an affiliation with the Celtics.

“I’m extremely excited about our enhanced partnership with the Celtics,” he said.

The Red Claws, despite missing the playoffs in all of their three seasons, are among the D-League’s model franchises, selling out nearly every home game and being among the league leaders in merchandise sales. They were honored recently with five of the league’s six annual business awards.

Their affiliation announcement came just five days after Dave Leitao left after a year as the team’s head coach and Jon Jennings, the man primarily responsible for bringing the team to Portland, stepped down as general manager and president.

Jennings was responsible for filling the team’s roster for its first three seasons. Leitao was Jennings’ choice to be head coach last year.

Ryan was joined at a press conference Thursday by Ainge and Dan Reed, president of the D-League.

Reed noted that such single affiliations — known as “hybrid affiliations,” in which the NBA team runs the basketball operations and the D-League team runs the business — have increased this year.

There are four other hybrid affiliations: the Houston Rockets with Rio Grande Valley, the Brooklyn Nets with Springfield, the New York Knicks with Erie and the Portland Trail Blazers with Idaho.

Six other NBA teams have single affiliations with D-League clubs, but those arrangements are different because the NBA teams do not have full control of the basketball operations.

“This partnership is indicative of an accelerating trend in the NBA Development League,” Reed said Thursday. “This trend has been extraordinarily positive, not only for the teams involved but the league as a whole.”

He called the Celtics-Red Claws deal “a natural evolution in what has already been a strong partnership between two strong organizations.”

Ainge said the search for a new coach will likely begin later this summer. “I do have some initial ideas,” he said, “but I can’t share that right now.”

Ainge said the Red Claws will not have a general manager in name, and all basketball decisions will be made by the Celtics’ front office, including Ainge; his son Austin Ainge (a former Red Claws’ coach and current director of player personnel for the Celtics); Ryan McDonough (Boston’s assistant general manager); and Mike Zarren (Boston’s assistant general manager and team counsel).

The Red Claws will use the Celtics’ offensive and defensive systems, so it will be easier to move players between Boston and Portland.

“I think that this opportunity creates a better chance for us to develop a better relationship,” said Ainge. “I think it’s better to have our own coach, who will be a member of our staff, who will be on the same page as our coach, Doc Rivers, and his staff … with the same goal in mind, to develop players without having to share the affiliation with other teams.”

The Celtics will fill the Red Claws’ roster through the D-League draft and free agents.

NBA and D-League rules will allow as many as three first-, second- or third-year NBA players to be on the Red Claws roster, as well as any NBA veteran who agrees to come down while on injury rehabilitation.

Ainge said the Celtics have wanted the new agreement for a while but couldn’t complete it because of priorities at the NBA level.

“I think we’re ready now,” he said. “Our team’s in a little different place right now. Our focus has always been on development, but I think it will just be increased a little more.”

Staff Writer Mike Lowe can be contacted at 791-6422 or at:

mlowe@pressherald.com

Twitter: MikeLowePPH