Tom E. Curran • E-mail

BOSTON - Ambling off the court at halftime of a preseason yawner against the New York Knicks comes Boston Celtics coach Doc Rivers. Crashing knuckles with an assortment of ushers and fans without making eye contact, Rivers is almost out of sight when a Celtics fan hurries to the metal rail above the tunnel.

Draping himself over the edge like human bunting, the 30-something man belches down at Rivers: "Let's do it again, Doc!"

Rivers raises his right hand in response. He keeps his eyes cast downward on his shiny shoes and vanishes from view.

Do it again, Doc? Just like that, huh? Repeat the 82-game, 67-win regular season and the 26-game playoff odyssey that ended with the Celtics' first title in 22 seasons? Do Celtics fans who wandered in from the cold to jump aboard the 2007-08 bandwagon have adequate appreciation for how hard doing it the first time was?

Do they realize how hard it will be for this team — built around the "Big Three" of Kevin Garnett, Paul Pierce and Ray Allen (combined age 96, combined experience 35 seasons) — to "do it again?"

The Celtics know. And they seem to take very seriously this business of defending their NBA crown.

"We don’t come in any less hungry or less driven," says Allen. "It’s no different having won. We’re not on country-club status now and feel we have to do any less than we did before. Most of us are not sitting on a pedestal and thinking we’re the best. This is a new year and has nothing to do with last year. It’s a new year and we have a new team."

On paper, the Celtics have as good a chance as anyone of hoisting the Larry O'Brien Trophy again. Cleveland, Detroit and Orlando are the most likely threats to Boston in the Eastern Conference. In the more-potent Western Conference, Utah, New Orleans, San Antonio, Phoenix, the Los Angeles Lakers, Houston and even Portland could emerge.

But none of those teams will be negotiating this season with the blessing and curse that comes with being defending champion.

"Won’t be easy, I’ll tell you that," warns Celtics guard Sam Cassell, who won back-to-back titles with the Rockets in his first two years in the league back in 1994 and '95. "When you are the champions, everyone will take a shot at you. Everybody. From teams that won 20 games to teams that won 50 games.

"We are at the top of the mountain and that’s something we have to understand. They’re coming. Everybody’s coming. Eve-ry-body’s coming! That’s why after my first championship, the next year we were the sixth seed (in the playoffs) because we didn’t know how hard everyone would come at us."

The Celtics' starting lineup will remain the same — Garnett, Pierce, Allen, center Kendrick Perkins and point guard Rajon Rondo — but the one big loss the team has to adjust to is the loss of veteran defensive stopper and three-point threat James Posey. Posey signed with the Hornets as a free agent, taking with him a selfless style that has helped him be a part of two championships (Celtics, and Miami in 2006).

Jim Rogash / Getty Images The Week in Sports Pictures The nation grieved for those hurt, killed and affected by the Boston Marathon bombings. After one of the suspects was caught on Friday — following a day-long lockdown and manhunt — sports returned to Boston over the weekend.

"One of the toughest things this team has to deal with is not having Posey,” says Celtics radio analyst Cedric Maxwell. "Who's going to be the one to take that charge? James Posey was always ready to do that. James was somebody you could count on hitting that trey at pivotal times to open up the floor. Who's going to do that?"

With fourth-year guard Tony Allen — a slasher and a very good defender — marksman Eddie House and bangers Leon Powe and Glen "Big Baby" Davis expected to be the primary bench players, the answer to Maxwell’s question isn’t obvious. None of them can do by himself the things Posey did.