When Chris Kiritsy purchased Boston Celtics season tickets two years ago they were one of the worst teams in the NBA.

He couldn’t even give the tickets away.

On Tuesday night he wouldn’t have sold them for anything. Instead, he invited Lakers fan and longtime friend, Bangor native Steve Averill, to come along.

The team’s success is making a lot of fans smile, including Kiritsy, a lifelong Celtics fan who witnessed the festivities firsthand at the TD Banknorth Garden in Boston as the Celtics won the NBA championship.

“I marvel. I think it’s one of the most remarkable turnarounds in sports history,” he said. “They went from the lowest depth last year to being at the pinnacle. It was a perfect night.”

Kiritsy played basketball at Bowdoin College in Brunswick and has cheered for the Celtics through many difficult seasons. He isn’t a fair-weather fan. After moving to Miami 13 years ago, he bought season tickets to watch the Miami Heat play, but never stopped rooting for the Celtics.

“I remember being in Miami and cheering for the Celtics even when the Heat were good, and people would look at me strangely,” Kiritsy said. “It didn’t matter to me. I’ve always been a steward of the Celtics. It’s a great organization. This is my team.”

Kiritsy moved back to Massachusetts recently and bought season tickets before the Celtics had traded for superstars Kevin Garnett and Ray Allen.

“Two years ago I bought season tickets and [the Celtics] were absolutely terrible,” he said. “But I didn’t care as much as other fans because I like to watch good players and I felt like Paul Pierce was exciting to watch.

“This year it was a bonus because you got to watch great players and they were winning.”

While Kiritsy never stopped cheering, his perception changed dramatically.

“I used to be more about the X’s and O’s,” he said. “When they’re winning you get more fanatically involved. Fan is short for fanatic, so if you’re a true fan you are going to be a fanatic and you’re going to be emotional and won’t be objective.”

Tuesday night it was Kiritsy’s friend’s turn to root for a losing team in a hostile environment. Averill, a former Celtics fan who played basketball with Kiritsy at Bowdoin, started rooting for the Lakers when he moved to L.A. 13 years ago. Kiritsy gave him a ticket to the game so Averill went dressed in a yellow Lakers T-shirt.

“I was a target for drunk and unruly fans and it got worse as time went on and they got more drunk,” Averill said. “We had a great time, though.”

Despite L.A.’s loss to the Celtics, a team he used to support, Averill is sticking with the Lakers. But he still feels good for the Celtics.

“There’s no changing stripes for me. I’ve made my move and sticking with it,” Averill said.

“I’m really happy for Kevin Garnett and Paul Pierce. It’s easy for me to feel happy for those guys. I don’t have that same lust-blood hatred for the Celtics as old-time fans do.”

Many current Celtics fans are basking in the glory now.

“The Celtics generated excitement from the beginning,” said Mike Webb, John Bapst’s girls basketball coach. “Along with the New England Patriots and Boston Red Sox, it’s a great time to be a sports fan in New England. Winning breeds winning.”

Webb said he didn’t used to follow the NBA very much because it didn’t promote the same team principles he did. But this year the Celtics emphasized defense and that caught Webb’s attention.

“They talk about defense and team basketball and hold each other accountable,” Webb said. “Those are things you try to teach as a [high school] coach. It’s a team game and when you get a group of guys who put the team first good things happen.”

Ted Woodward, the University of Maine’s men’s basketball coach, agreed.

“The Celtics really brought, not only talent, but great character,” Woodward said. “They were single-purposed in what they wanted to accomplish. That was a huge step and they did a great job.”