Despite battling a head cold, it was big turnaround after James managed just 15 points on 5-for-15 shooting while being harassed by Luol Deng in Game 1.
"I put it all on the line on the line tonight and did whatever it took for our team to win," James said.
Wade also looked more like a superstar after scoring 18 on Sunday. Udonis Haslem, whom Heat coach Erik Spoelstra called "an absolute championship warrior," provided a spark off the bench with 13 points, and the Heat beat the Bulls for the first time this season even though Chris Bosh scored just 10 after pouring in 30 in the opener.
Derrick Rose led Chicago with 21 points but scored just two in the fourth quarter. Deng, the only other Bulls player in double figures, added 13 but had just four after the opening period.
Joakim Noah had nine points but only eight rebounds. Taj Gibson provided a spark in the fourth quarter, scoring all of his eight points. Carlos Boozer, however, was a non-factor with seven points and eight rebounds.
The Bulls missed countless layups and got outshot 47.1 percent to 34.1. They were just 3 of 20 on three-pointers and 16 of 26 at the foul line while getting beat on the glass.
They had no answer for James down the stretch, either, and came up short when it looked like they might find a way to pull the game out.
"We played a low-energy offense, a low-energy defense and the result was not good," coach Tom Thibodeau said.
The Heat led by 11 late in the third, only to see the Bulls wipe it all out all in the fourth, with Gibson providing a big spark.
He cut it to 71-69 early in the fourth with back-to-back jumpers for his first points of the game, pumping both arms after the second shot went in.
Then, he tied it at 73 with 7:16 left after Haslem lost the ball out of bounds, drawing more roars from the crowd, but the teams traded misses for about 3 minutes before James put Miami ahead with a three. Then he scored again with 3:15 left to make it 78-73.
Gibson delivered a slam over three defenders and got fouled by Wade to make it a three-point game with 2:29 left, but missed the free throw.
James then put back his own miss and nailed a 20-footer to make it 84-75 with 47 seconds left.
"That fourth quarter is going to epitomize this entire series," Spoelstra said. "It's an absolute street fight for both teams."
Before the opening tip, former Bulls forward Dennis Rodman, who is heading to the Hall of Fame later this year, presented the game ball to a raucous ovation.
Also in attendance was Chicago Bears defensive end Julius Peppers.