The Heat, who have opened the new season with a revamped roster that has taken little time to mesh, followed up their 25-point victory over Phoenix on Monday with another impressive effort.
Miami (4-1) made 10 three-pointers and befuddled the Nets with their passing, breaking the game wide open in the third quarter.
Shane Battier and Mario Chalmers made back-to-back three-pointers to cap a 10-0 run that put the Heat up 64-46 in the third, and James closed the quarter with a three-pointer of his own that stretched the lead to 23.
"As long as the guys have the right mindset for this and the maturity that if we play our game and hit the open guy, then you can see the strength of our offense," Heat coach Erik Spoelstra said.
Deron Williams scored 14 points for the Nets.
After making a big splash in the off-season by re-signing Williams along with Joe Johnson and relocating to Brooklyn, the Nets have yet to make their mark on the court.
"Nobody said we're on Miami's level. Nobody ever said it," said Brooklyn coach Avery Johnson.
"So we're not there yet. We're definitely not there after three games of the regular season."
The Nets were hurt by 19 turnovers which helped to feed the Miami offense.
The Heat also got strong performances from their newcomers with Rashard Lewis scoring 13 points on 6-of-9 shooting, while Ray Allen, having already won a game with a last second shot against Denver on Saturday, finished with nine points.
Later in the evening, four-time NBA champions San Antonio Spurs crashed to their first defeat of the season as the Los Angeles Clippers dazzled with high-flying dunks and tight defence on the way to a crushing 106-84 win.
Unbeaten in their first four games, the Spurs were no match for an energised Clippers team at a sell-out Staples Center where twice All-Star Blake Griffin was a tower of strength, recording a game-high 22 points along with 10 rebounds.
Clippers centre DeAndre Jordan weighed in with 20 points and 11 rebounds while back-up guard Eric Bledsoe contributed 15 points and Matt Barnes, also off the bench, 12.
"Tonight we were so successful because of our defence," Clippers point guard Chris Paul, who totalled 10 points and 12 assists, told reporters. "One thing we said before we ran out tonight was, 'Let's just have fun out there.'
"When you defend and stop teams, that is what basketball is all about. We know that we can score, but it is actually fun to stop teams and see them get frustrated."
Seven Clippers players scored in double figures as the home team snapped a two-game losing streak in scintillating style, out-rebounding the Spurs 46-29 and out-shooting them from the field by 55.4 percent to 41.1.
Guard Danny Green poured in three three-pointers to lead the Spurs with 12 points but veteran forward Tim Duncan, with 10, was his only other team mate who got into double figures.
San Antonio, who play their next three games on the road, slipped to 4-1 for the season while Los Angeles improved to 3-2.
"The Clippers played well and that's why they won," said San Antonio coach Gregg Popovich. "They were more emotional, more aggressive. We hung in there for a half but after that we didn't play with the same intensity as they did, and it showed.
"We sucked on defence. They were aggressive. They got to the hole, they beat us in the break. Every aspect of our defence was poor."
The Spurs, who had crushed the Indiana Pacers 101-79 on Monday for a franchise-best 4-0 start, raced into an early 7-2 lead but power forward Griffin led the Clippers charge as the home team came roaring back to take control.
A Barnes three-pointer put them ahead 29-18 midway through the second quarter and, despite an unanswered seven-point San Antonio run capped by a Tony Parker floating jump shot, Los Angeles led 47-41 at half-time.
With Jordan thrilling the home crowd with a series of slam dunks and Bledsoe shining with several jinking drives to the basket, the Clippers padded their advantage to 82-62 heading into the final quarter.
There was no way back for San Antonio after that as the Clippers dominated both ends of the court, and Griffin latched on to three 'alley oop' dunk shots to rub salt into Spurs' wounds before leaving the game with 4:47 remaining.
Watched by a crowd of 19,060 that included American boxer Floyd Mayweather Jr., the Clippers gained a measure of revenge after being swept by the Spurs in the second round of the playoffs last season.
"We came out with the mindset that we had something to prove," said Griffin. "We felt we owed it to ourselves to come out and be on our game offensively and, more importantly, defensively.
"We have a lot of guys that can score but when we lock in defensively, that leads to easy baskets and really gets us going.
"We were active, we were talking. I thought we did a great job of trying to hustle and make up for our mistakes."