Then he joined the Miami Heat, and things only got worse.
Miami has lost seven of eight on the parquet floor since James arrived to form a superteam modeled after the new Big Three that hung the Celtics' unprecedented 17th NBA championship banner.
The Heat will need a victory here in Game 6 of the Eastern Conference finals on Thursday night to avoid a fourth straight loss to the Celtics, a fifth straight loss in Boston and a second straight year of failed promise from the trio of James, Dwayne Wade and Chris Bosh.
''We plan to win the ballgame. We've got to win. That's all we've got to do,'' Wade said Wednesday before the Heat boarded a plane to return to Boston. ''Can't listen to the noise. I'm not. I'm sure our team is not. We're just focused on winning this ballgame.''
It was in Boston that James said goodbye to Cleveland, ripping off his jersey as he left the court after Game 6 of the 2010 Eastern Conference semifinals after the Celtics spoiled the two-time defending NBA MVP's best chance to win a title with his hometown team.
But Miami has had even bigger struggles in Boston, winning just once on the parquet since Kevin Garnett, Paul Pierce and Ray Allen joined forces. The Celtics knocked the Heat out of the playoffs in the first round of the 2010 playoffs, one series before eliminating James' Cavaliers. (The Heat did eliminate the Celtics from the playoffs last year, but they needed just one win in Boston.)
In all, Miami has lost 15 of its last 16 regular-season games in Boston.
''Why would you think about that? What does it do for you? Is it going to change anything? No,'' Wade said. ''You've got to go out and try to play - each game is its own. You can't say, 'Oh, well, we're down one point and we've lost 15 out of 16 here. We're not going to win.'
''It doesn't work that way.''
Miami finished seven games ahead of the Celtics in the lockout-shortened regular season to earn home-court advantage, then gave it back on Tuesday night when Boston beat the Heat 94-90 to win Game 5.
That means the Celtics just need to win at home on Thursday to advance to the NBA finals for the third time in five years.
''I know how much pain this team has given me over the years,'' James said. ''I think I guess it's only right that we will be going up there in an elimination game. In order for us to keep our season going, we have to win in their building.''
That would force the series back to Miami for a decisive seventh game, giving the Celtics a fallback if they should falter at home.
But they're not interested in that.
''We have one home game left, and that's it in this series,'' coach Doc Rivers said Wednesday. ''We have to understand that, and we have to come with that sense of urgency. Our guys understand that, and I think so does Miami.''
The Celtics would also like to avoid a Game 7 so they can rest their banged-up regulars, including thirtysomethings Ray Allen, Paul Pierce and Kevin Garnett.
Allen, who missed the first two games of the postseason because of bone spurs in his right ankle, left Game 5 in the third quarter when his ankle stiffened but returned in the fourth and sank two free throws with 14 seconds left to give Boston a four-point lead.
''He just said it's locked on him again,'' Rivers said. ''That's happened a couple of times. He needed our doctor to maneuver it ... so he can run again.''
Rondo dislocated his left elbow in last year's second-round playoff series against the Heat. He appeared to injure the same arm early in Tuesday's game, adjusting the sleeve he wears on it and seeking assistance from the Celtics' trainer.
But he finished with seven points, 13 assists and six rebounds - one of them when he slapped a loose ball away from James to Mickael Pietrus for a 3-pointer.
Rivers said he didn't know what was wrong with Rondo's elbow - and didn't want to know.
Bosh returned after missing the nine playoff games with a lower abdominal strain from the opener of the conference semifinals against Indiana. He had nine points and seven rebounds in 14-plus minutes but was not on the floor down the stretch when the Celtics came back to win 94-90.
Bosh said Wednesday that he is ''99 percent'' and that he did not ask to be held out in the fourth last night.
''I think he'll be able to handle a bigger load of minutes,'' Heat coach Erik Spoelstra said. ''It'll be based more on how he feels during the game.''
- Miami Heat
- LeBron James