Associated Press

WALTHAM, Mass. — Paul Pierce and Kobe Bryant were playing pickup basketball in a UCLA gym last summer, a couple of frustrated NBA stars trying to sweat away the memory of a disappointing season. Talk soon turned to trades.

Bryant had lashed out at Lakers management for assembling a team that hadn’t won a playoff series in three years. Boston had gone four years, and Pierce worried that he might become the trade bait that kick-starts the rebuilding process.

‘‘I remember being in the gym with Kobe, and me and him were arguing over who was going to get traded first,’’ Pierce said Monday after the Celtics held their first practice in preparation for the NBA finals.

‘‘He went public about getting traded, … and I was like, ’Shoot, I’m going to getting traded before you,’ and betting that it would happen. That’s what so crazy, now we’re both here sitting in the finals, where a year ago we were both in the gym.’’

No one wound up paying off the undisclosed stakes. Instead, both players stuck with the only NBA teams they’ve ever known and earned the chance to play for a championship.

Game 1 of the best-of-seven series is Thursday night in Boston.

Bryant has already won three NBA titles, teaming up with Shaquille O’Neal to win in consecutive years from 2000-02. They made one more run at it in 2004, losing to Detroit in the finals before O’Neal was traded away; it was Bryant’s team, for better or worse.

The Lakers missed the playoffs the next year for just the second time in almost 30 years, followed by two straight first-round losses that left Bryant wondering.

Then, he snapped.

Bryant called the team’s front office a mess and said he wanted to be traded. Then he said he didn’t. Then he said he did.

In the middle of the hubbub, he found himself sharing a post-pickup swig of water with Pierce

‘‘Both of us kind of being in the same boat — the irony that we’re both in the finals is cool,’’ Bryant said after the Lakers practiced at their workout facility in El Segundo, Calif., on Monday. ‘‘It’s good for both of us to be here. He’s a great guy.’’

Pierce had his own problems.

The Celtics had been accumulating young talent like Al Jefferson, Delonte West, Ryan Gomes, Rajon Rondo and Kendrick Perkins, but they had few wins — 24, to be exact — to show for it. When the draft lottery didn’t yield a potential star like Greg Oden or Kevin Durant, the team’s next title seemed far in the future.

‘‘We were at a point where we were frustrated with the moves. The most obvious thing to do was to trade your star player for some young pieces and rebuild from there,’’ said Pierce, the longest-tenured Celtics player since the original Big Three.

‘‘I pretty much thought it was over. I can’t even explain it. I thought I was going to be a Los Angeles Clipper; I thought I was going to be anywhere but the Celtics,’’ he said. ‘‘All I know is if I wasn’t a Celtic, right now I’d be home.’’

Instead, the Celtics built around Pierce, adding Ray Allen and Kevin Garnett in one of the most dramatic overhauls in league history. The team that went 24-58 with a bunch of young players won 66 games this year and put the Celtics in the finals for the first time since 1987.

‘‘I get the pleasure of seeing him play every night, but they could have went a different way,’’ Garnett said. ‘‘I’m glad to see the organization stand behind a guy who has been able to give his all for them, for them to step up and actually give him some players and some help, so that he can reach his goals as a basketball player.

‘‘When you’re a competitor, man, the one thing you want is a chance. They obviously went out and made the right deals. So my hat goes off to them.’’

The Lakers made a deal of their own, acquiring Pau Gasol from the Grizzlies on Feb. 1 to help turn around a team that had shown promise before losing five of seven. After Gasol joined them, the Lakers won 12 of their next 13 games and went 28-9 the rest of the way before going 12-3 against Denver, Utah and San Antonio in the playoffs.

That led them back to Boston, archrivals from 10 previous championship series; the Celtics have won eight. Celtics coach Doc Rivers, who watched the Bryant drama unfold from afar, said he wouldn’t want it any other way.

‘‘I was just happy he stayed out West’’ where he would only face Boston twice a year, Rivers said. ‘‘But I’m glad it worked out the way it worked out. Just like Paul Pierce is a Celtic, Kobe is a Laker.’’