The Boston Celtics got the best of James twice when he was with the Cleveland Cavs. In 2008 the Celtics got the best of James in the second round, on their way to banner 17. In 2010, the Celtics went in as underdogs against James and the Cavs. LeBron led the Cavs to the best record in the East, and in the NBA overall. The Celtics went into the second round series off a first round series win over Wade and the Heat.
In the second round for the Celtics, they were embarrassed on their home floor against the Cavs falling down 2-1 in the series. After Rondo's legendary performance in game 4. The Celtics would go and win the final two games in the series, sending the NBA title favorites packing. James was crushed, and it forced him to team with Wade and Bosh in Miami so he could get past the Celtics.
The Heat and Celtics would squared off in 2011 in the second round,and in the 2012 Eastern Conference Finals. The Celtics nearly derailed the start of this 2-peat when they held a 3-2 series over Miami in the ECF's. The Celtics couldn't closeout at home in game 6, and the Celtics were unable to shock the Heat on their home floor in game 7. There is no question that the Celtics forced the Heat to form in some ways, and there is no question that the Celtics forced the Heat to get tough for their past two titles.
"We played Boston a lot, and they made it more than just about basketball, and they beat us in the mental game as well as the physical game," Dwyane Wade told reporters. "We learned that the only way we're going to beat them is if we beat them playing the game of basketball. They're great at that mental game.
"So from that point, we try to leave that alone. We try to beat you at basketball. We don't go into the back‑and‑forth talking because that's not what we're here for, and that's not going to win us a game. So we try to beat you at basketball."