Dwyane Wade added 15 points and Miami never trailed, leading by 23 at one point.
"We try to get better every single day, every single game," James said. "When you do that and go out and play the type of game that you are capable of playing, you can be satisfied with the results. And that's what we've built over the years."
Only the Celtics and Lakers franchises have been to the NBA Finals in four straight seasons. The Heat now have three chances to join that club, starting with Game 5 at Indiana on Wednesday night.
"We got outplayed by the Heat," Pacers coach Frank Vogel said. "I wasn't disappointed in our fight. I was disappointed in the result."
Paul George scored 23 points and David West added 20 points and 12 rebounds for the Pacers, who got 15 points from George Hill. But Lance Stephenson who made news in the days between Games 3 and 4 by suggesting he was in James' head was held to nine and 7-foot-2 center Roy Hibbert was scoreless in 22 minutes for Indiana.
"I was trying to get into his head," Stephenson said, referring to James. "I guess he stepped up and got the win. I can take the heat."
The heat, maybe.
The Heat, maybe not.
Miami has won the last three games in the series, and going back to the point in Game 3 when the Heat trailed by 15, they have outscored the Pacers by 39 points in a span of about 6½ quarters.
The Pacers won two elimination games in the first round against Atlanta, and need to win three more if their yearlong plan of topping Miami as kings of the East is going to become reality.
The odds are obviously stacked against them. When holding a 3-1 lead, Miami is 8-0 in Game 5s over the past four postseasons.
"We have a chance to play an NBA game on our home floor," West said. "We are going to try to do something that's very tough."
Bosh scored the game's first eight points, making a pair of 3-pointers and ending a series-long funk. He had scored exactly nine points in each of the first three games of these East finals and was held under 10 points in each of his last seven playoff games against Indiana.
But he came out flying, and probably not coincidentally, the Heat finally had a good start.
"I told him he was going to have a great game," James said. "We got off to a fast start because of him."
Miami won the first quarter for the first time in the series, going up 27-19 and helped in part by a late 3-pointer from Shane Battier with replays showing Vogel moved down the sideline toward the Heat forward as he shot from near the Indiana bench.
If nothing else, at least he was trying to beat Big Brother.
Much as he did Sunday, Vogel used the big brother-little brother analogy with his team, trying any way to urge the Pacers to break through against the team that has ended their season in each of the past two years.
"He's got to make a decision at some point in his life, that no matter what, we're not going to lose this fight anymore," Vogel said, likening the Pacers to the little brother in that scenario. "We're at that point."
The fight isn't over.
But it was awfully one-sided for long stretches of Game 4.
Oklahoma City's Serge Ibaka expects to play on Tuesday in Game 4 against San Antonio. › C2
Heat 102, Spurs 90
Indiana 19 25 20 26 90
Miami 27 22 31 22 102
George 8-16 4-7 23, West 9-18 2-2 20, Hibbert 0-4 0-0 0, G.Hill 5-10 1-2 15, Stephenson 3-7 3-5 9, Scola 6-8 0-0 12, Butler 1-3 0-0 3, Watson 1-2 0-0 3, Mahinmi 2-3 1-1 5, Copeland 0-0 0-0 0.
Totals 35-71 11-17 90.
James 13-21 4-4 32, Lewis 0-5 0-0 0, Bosh 7-12 8-10 25, Chalmers 2-2 0-0 4, Wade 4-12 7-7 15, Haslem 1-3 3-4 5, R.Allen 2-8 4-4 9, Cole 2-4 2-2 7, Battier 1-2 2-3 5.
Totals 32-69 30-34 102.
3-Point GoalsIndiana 9-21 (G.Hill 4-7, George 3-9, Butler 1-2, Watson 1-2, Scola 0-1), Miami 8-24 (Bosh 3-5, James 2-3, Battier 1-2, Cole 1-2, R.Allen 1-5, Wade 0-2, Lewis 0-5). Fouled OutNone. ReboundsIndiana 44 (West 12), Miami 39 (James 10). AssistsIndiana 18 (West, G.Hill, Stephenson 4), Miami 16 (James 5). Total FoulsIndiana 27, Miami 17. TechnicalsHibbert, Indiana Coach Vogel. A19,874 (19,600).