James scored 27 points with 10 assists and 11 rebounds for the 31st triple-double of his career and his third since his move as a free agent to Miami prior to this season.
Chris Bosh added 24 points and 13 rebounds for the Heat and Dwyane Wade chipped in 18 points despite being slowed by a sore knee.
Even more importantly, the Heat pressured and harried the Kobe Bryant-led Lakers, preventing them from finding any offensive rhythm.
"That's Miami Heat basketball," James said. "We just try to go out and defend. We know that's going to give us the best chance to win. When we're in tune like that defensively — five guys on a string, we're all helping each other out — we're a pretty good team." James played a controlled game, despite receiving a technical foul shortly before halftime as he jockeyed for position under the basket with Los Angeles' Ron Artest, who also received a technical.
His demeanor reflected the poise of the entire Heat team, who led 20-14 after a first quarter in which they held both Bryant and Pau Gasol without a field goal.
"The most important thing, I think we really got to our identity, defending and disrupting as much as we could," said Heat coach Erik Spoelstra, whose team improved to 23-9. "It got us into a rhythm offensively.
"Even though we only had four fast-break points a lot of our opportunities were in early offense and our confidence just seemed to grow when we were able to get consecutive stops and rebound the basketball." It was the first meeting between the two teams since James, Wade and Bosh elected to link up in Miami as free agents, forming a superstar trio that immediately had the Heat tabbed as title contenders.
James and Bryant had both said the much publicized holiday match-up was just one more contest in the long NBA regular season.
But at the end of the game the two could be seen exchanging words on the court.
"We're just two competitors, two guys just trying to will their team to victory," James said.
Bryant, who was unhappy with his own teammates by the end, said sourly: "I just asked him what he got for Christmas." Bryant and Gasol scored 17 points each for the Lakers. Lamar Odom added 14 points and nine rebounds for Los Angeles, who have lost two in a row at home after Tuesday's upset against Milwaukee.
Bryant made it clear he believes some of his teammates aren't playing with enough urgency and focus as they pursue a third straight championship. The Lakers own a 21-9 record, but haven't impressed against opponents with winning records.
"The game has to be the most important thing," Bryant said. "You have to focus on it. You have to play every game like it's your last. You have to be attentive to what's going on.
"You don't just have two rings and say 'OK, we're satisfied with what we've got.' "I'm not rolling with that," Bryant said. "I'm not going to let that slide. We need to get into gear."
In Orlando, the hosts ended yet another long winning run, beating Boston to snap the Celtics' 14-game streak.
Having halted San Antonio's 10-game run in the previous game, the new-look Magic got into its stride in the second half after Boston had taken a 12-point lead.
Brandon Bass scored 21 points and Hedo Turkoglu added 16 for the Magic, who took a measure of revenge for last season's defeat by Boston in the Eastern Conference finals.
Kevin Garnett had 22 points for the Celtics in their first loss in over a month.
In New York, the home team limited Chicago to just two baskets in the first 10 minutes of the fourth quarter, setting up a victory over the Bulls.
Amare Stoudemire and Raymond Felton each scored 20 points for the Knicks, the NBA's highest-scoring team but 28th in defense. Stoudemire anchored the defensive effort, grabbing 10 rebounds and blocking six shots Carlos Boozer had 26 points and 19 rebounds for the Bulls.
In Oklahoma City, NBA scoring leader Kevin Durant had a season-high 44 points - 21 in the third quarter - for Oklahoma City in the win over Denver.
In the Thunder's first Christmas game, Durant was 14 of 20 from the field and raised his scoring average to 28.1.
James Harden added 21 points for the hosts.
Denver played for the second straight game without star Carmelo Anthony following his sister's death Wednesday.
Chauncey Billups led the Nuggets with 30 points.
In Oakland, Golden State scored 11 straight points to erase a six-point deficit in the fourth quarter and beat Portland in its first Christmas home game.
Monta Ellis scored 39 points and David Lee added 21 points for the Warriors, who posted rare back-to-back wins in the team's first Christmas home game.
Wesley Matthews led Portland with 25 points.
