Chris Bosh scored 25 points and James added 10 rebounds and five assists as the Heat seized a 3-1 lead in the best-of-seven Eastern Conference final.
Miami can clinch another berth in the championship series with a victory in game five Wednesday at Indianapolis.
“It’s going to take a better game than we had tonight,” James said. “We have to get better every game.”
Miami or Indiana will face either San Antonio or Oklahoma City in next month’s NBA Finals.
The Heat improved to 8-1 at home against Indiana over the past two seasons and stretched their overall home playoff win streak to 10 games.
Miami led 49-44 at half-time, but the Heat dominated the third quarter, thanks in part to 14 points from James, and stretched the margin to 80-64 entering the fourth quarter.
A 13-1 Indiana run pulled Indiana within 95-84 but the Heat, who never trailed, kept the top-seeded Pacers at bay over the final minutes.
Bosh, who had struggled to find his scoring touch against the Pacers, scored 17 points in the first 17 minutes.
“I thought that was going to happen today,” James said. “I told him he was going to have that kind of game. We got off to a great start because of him.”
– Back to basics for Bosh –
Bosh said the key to victory was not taking too many shots or pressing too hard.
“Sometimes it’s all about simplifying everything and getting back to the basics,” Bosh said. “As a scorer you want to see the first shots go in. That helped me be aggressive as the game went on. I was able to put the cerebral stuff to bed and just go out and play the game.”
The Heat also made a starting lineup switch, adding Rashard Lewis to alter the individual matchups with the Pacers and help spark Bosh’s scoring.
“It was good to get off to a good start,” Bosh said. “We played the game we wanted to play from beginning to end. We changed up their looks and gave them something to think about. We were able to get into our rhythm and dictate the tempo.”
Paul George led Indiana with 23 points while David West had 20 points and 12 rebounds and George Hill contributed 15 points.
Miami outscored Indiana 30-11 at the free throw line and George incredibly claimed that was the reason the Heat won, even though the Pacers never led.
“We outplayed them,” George said. “They won this game at the free throw line. But I thought we outplayed them. It’s just demoralizing when the game is lopsided. They made 30 free throws. That put them over the edge.”
James responded by saying, “We only had five turnovers and we scored 20 points off their turnovers. That’s got nothing to do with free throws.”
Indiana’s Lance Stephenson, who said he felt his taunts were getting inside of James’ head, managed only nine points.
“Once the ball went up, all that stuff was behind him,” Indiana coach Frank Vogel said. “He got into foul trouble and didn’t get into a rhythm.”
Stephenson wasn’t willing to recant about having any impact on James.
“Tonight was his night to step up and show he was awesome and he did that tonight,” Stephenson said. “I guess he stepped up and they got the win.
“I can take the heat. I can take the fire. He got the win. His teammates helped him.”
James laughed at the idea, saying, “I got a smirk out of it,” and adding, “I didn’t need any motivation. I was motivated enough to get back to the finals. That’s what it’s all about.”
Stopping the four-time NBA Most Valuable Player is the Pacers’ main goal and likely their only hope to win the final three games and advance.
“We’ve got to do a lot to keep in front of him,” Vogel said. “He’s the best player in the world. We’ve got to make it difficult for him.”