WALTHAM, Mass. – The act debuted on media day, when cameras and notebooks descended upon the Celtics as they opened training camp in September.

Rather than separate for individual interviews, the new Big Three took the podium together. Paul Pierce, Kevin Garnett and Ray Allen met the media as a package – three stars mugging and joking and laughing.

“We’re trying to build some chemistry,” Pierce said.

As the Celtics begin their season Friday night against the Washington Wizards, there already are plenty of built-in expectations.

The moribund franchise overhauled its roster after failing to land one of the top two lottery picks in the draft. Rather than bemoan the failure to get Greg Oden or Kevin Durant, the Celtics acquired Allen and Garnett in a pair of blockbuster trades.

So after nine seasons, Pierce, 30, has a superior supporting cast and the Celtics are a legitimate title contender for the first time since Larry Bird was wearing green.

“I think it’s a good feeling for us as players, especially those of us that have been in such tough situations over the last couple of years,” Allen said. “Having expectations is not a bad thing.”

Allen, 32, has been a prolific scorer for 11 seasons, but he has only been on four playoff teams and hasn’t been in the playoffs in two years. Garnett, 31, has been among the NBA’s elite players for most of his 12 seasons, but hasn’t been in the playoffs in three years.

So when they arrived in Boston, they couldn’t help but eye the championship banners hanging in the TD Banknorth Garden.

“You feel the history here,” Garnett said.

The Celtics haven’t won a title in 21 years, so the fans are as hungry as the stars. Allen, who lives in Connecticut, understands the anticipation better than anyone. Garnett is so intent on winning that, despite being the team’s best player, he has refused to isolate himself from the rest of the team, only doing interviews and photo shoots with Allen and Pierce.

“We’re all similar in a lot of ways … we’re all passionate,” Garnett said. “The three of us have a high competitive spirit. The three of us hate to lose.”

In the first press conference at media day, Garnett stroked his green Celtics jersey and said it felt different than any jersey he has worn. Allen smiled and said that has been common conversation between the players.

“No offense to the teams we played on prior to this,” Allen said. “But we always comment on how much better this feels than the last team.”

So who is the leader? Garnett has shown leadership by keeping his new running mates by his side for every appearance. Allen has shown quiet leadership by insisting the three stars have a common goal. Pierce, the captain, has the history and credibility with the franchise.

At their recent exhibition game at Mohegan Sun Arena, the three sat with each other at the end of the bench. Garnett and Pierce were not playing, so they huddled through the game and commented on the play to one another. During timeouts, Allen conferred with Pierce and Garnett, and sat with them when he left the game.

After the game, Garnett and Pierce lingered outside the locker room together while Allen spoke to reporters.

“We’re going to be around each other a lot, on and off the court,” Pierce said.

Starting Friday night, we’ll see how they jell on the court when the games matter. The responsibility of distributing the ball to the elite scorers falls with second-year point guard Rajon Rondo, who has been praised by Garnett.

Rondo, 21, averaged 6.4 points and 3.8 assists in 78 games last season, but shot 41.8 percent, including 20.7 percent from three. Coach Doc Rivers said Rondo is mature enough handle the bulk of the minutes at point guard, but finding capable backup might be the problem.

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In fact, the entire second unit is work in progress. Rookie Glen Davis, veteran James Posey, and second-year forward Leon Powe are the reserves up front. Tony Allen, coming off knee surgery, will see minutes in the backcourt along with Eddie House (8.4 points for the Nets). Scot Pollard, who missed much of training camp with a sprained ankle, is the backup for center Kendrick Perkins.

So while the Celtics are being hyped as a title contender, there are questions beyond the Big Three. Ray Allen welcomes the expectations, but says the veterans know nothing is guaranteed.

“We still have to go out, live the process of trying to make this a great team,” he said. “It’s not just spoken and then we become one. We have to work at it.”

And Rivers, who has gone through a youth movement, is cautious.

“We have great names,” Rivers said. “But we have not won a game.”