BOSTON — LeBron James finished having his way with the Boston Celtics, and now it was the fans’ turn.

“BOO!”

So much for home-court advantage.

The Cavaliers took that, and whatever good feelings the Celtics had from their strong play in Cleveland, with a 124-95 victory on Friday night, handing Boston its worst home playoff loss and taking a 2-1 lead in the best-of-seven Eastern Conference semifinals.

James scored 21 of his 38 points in the first quarter, helping the Cavs wrap this one up even before many of the fans in green jerseys had taken their seats.

“Aggression was my mindset,” James said. “It was my mindset to come out really aggressive and just dictate tempo from the start of the jump and I was able to do that.”

James was 8 of 10 from the field in the first quarter and the Cavs shot well above 60 percent for most of the game before finishing at 59.5 percent. They led 65-43 at halftime, when the Celtics trudged off the floor to those loud jeers.

“We told our guys, you knew he was going to grab the ball and he was going to attack all game, especially early, to get his guys involved,” Celtics coach Doc Rivers said. “And he did it, but I didn’t think we gave any resistance, you know?”

Showing no ill effects of a strained and bruised elbow that was the talk of Cleveland during the three-day layoff since a Game 2 loss at home, James finished with eight rebounds and seven assists. The 21 points in a quarter was a franchise postseason record.

“I know I’m going to hear a lot about the elbow, but I’m here to play basketball and give our team a chance to win,” James said. “We knew how important it was to come out and play aggressively after giving away Game 2.”

Antawn Jamison had 20 points and 12 rebounds for Cleveland, while Shaquille O’Neal added 12 points and nine rebounds.

Rajon Rondo had 18 points and eight assists for Boston, but some of his star teammates struggled. Paul Pierce shot 4 of 15 and Ray Allen was 2 of 9.

“Offensively we didn’t have anything,” Allen said. “We didn’t start the game, didn’t move the ball around, like getting good looks. It was just snowballing for three quarters.”

The Celtics missed 10 of their first 13 shots, hitting just 27 percent in the first quarter to spot Cleveland a 21-point lead. The Cavaliers shot 67 percent from the field in the first and Boston was never able to recover.

The Celtics’ previous worst home playoff loss was 97-70 to Indiana on May 7, 2005, in Game 7 of the first round.

“It was great to see LeBron set the tone from the jump,” Cleveland coach Mike Brown said.