James scored 21 of his 38 points in the first quarter to help Cleveland beat Boston 124-95 on Friday night, handing the Celtics their worst home playoff loss ever and taking a 2-1 lead in the best-of-seven Eastern Conference semifinals.
Showing no ill-effects of an elbow problem that was the talk of Cleveland during the long layoff, 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."
Rajon Rondo, who had 19 assists in Boston's Game 2 victory on Monday, had 18 points and eight assists.
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 59 percent for the game -- and Boston was never able to recover.
"It was great to see LeBron set the tone from the jump," Cleveland coach Mike Brown said. "And the rest of the team followed."
Game 4 is Sunday, and the Celtics need a victory to split their home games and assure themselves of another.
James wore a black sleeve on his right elbow, which became a concern after he shot a free throw left-handed in the closing minutes of Cleveland's first-round playoff clincher against Chicago. But he went 8 of 10 from the field in the first quarter -- most of them mid- to long-range jumpers -- and after that it didn't matter.
"I think he's healthy," said Celtics coach Doc Rivers, who has been dismissive of James' injury. "His elbow looked very good tonight. So enough with the elbow injury. I think we can go ahead and focus on basketball."
The Celtics had high hopes for an upset of the 61-win Cavaliers after taking Game 2 in Cleveland to swipe the home-court advantage. But Cleveland earned it back in Game 3, needing just one quarter to silence the Boston crowd that grew even more downcast when the Red Sox and Bruins also fell behind early -- and then lost.
The fans booed when Boston left the court at halftime down 65-43. And they cleared the building midway through the fourth, when Rivers pulled his starters and James headed to the bench to rest his strained and bruised right elbow.
"That was embarrassing. That's embarrassing when you lose at home like that," said Paul Pierce, who scored 11 points on 4-of-15 shooting and didn't make his first basket until midway through the second quarter.
"We just let our guard down. ... You've got to know the Cleveland Cavaliers are going to come in here with all the urgency in the world. They took the fight to us early, and we didn't respond to it."
James scored eight straight points to make it a 10-point lead midway through the first, and seven points during an 11-0 run that made it 36-15 with 19 seconds left in the quarter. Cleveland led by 24 points in the second quarter, 30 in the third, and never by less than 20 in the entire second half.
"He was playing H-O-R-S-E," Rivers said. "We were awful. We just didn't play with the same intensity they did. They played with a Game 7 mentality."
The national anthem was sung by sandal-wearing Grateful Dead guitarist Bob Weir. ... The Celtics had a moment of silence for Bobby Vines, a 45-year-old sales account executive who died after a lifelong battle with sickle cell anemia. ... The NBA record for points in a quarter of a playoff game is held by Sleepy Floyd, who had 29 in 1987 for Golden State. ... James reached 2,000 playoff points in his career.