The 18-game streak ties the seventh longest in NBA history, and is the league's best since the Boston Celtics won 19 straight during the 2008-09 season. Miami will try for No. 19 when it hosts Atlanta on Tuesday night.
The win also gave Miami (47-14) a victory over every NBA team this season. The Heat lost both previous meetings with Indiana.
David West scored 17 of his 24 points in the first half for the Pacers, who fell nine games behind Miami in the Eastern Conference standings. Roy Hibbert scored 15, D.J. Augustin had 14 and Paul George scored 10 for Indiana.
James' previous season-low was 15. He still finished with seven assists and six rebounds for the Heat, who held a 27-15 edge in points off turnovers and finished the game shooting 56 percent compared with 41 percent by Indiana.
Chalmers needed only nine shots to get his 26 points, going 5 for 6 from 3-point range and making all seven of his free throws. He also grabbed seven rebounds, a season high.
There may have been touches of gamesmanship beforehand. Things like the Pacers coming out for warm-ups and choosing the basket that the Heat typically use, or just about every starter keeping those pleasantries before tip-off such as handshakes and hugs at an absolute minimum. And there were moments of physicality: an extra nudge here or there. But nothing near the level of those body-flying, blood-drawing clobberings that came during last season's Eastern Conference semifinals.
Then again, that series was competitive throughout. This game was essentially over just after halftime.
Miami led by nine after the opening quarter, the second-largest deficit the Pacers faced after 12 minutes all season. Indiana hardly folded; the Pacers used a 24-14 run to get within two when West scored with 2:57 left before the half. The margin was still only six in the final minute before intermission.
But the Heat couldn't have scripted a better final 6.9 seconds of the half.
After a deflection sent all the defensive matchups askew, James found himself being guarded 1-on-1 by Hibbert, so he simply drove past the 7-foot-2 center for a slam. Wade then stole the ball from George near midcourt with about 3 seconds left, took a couple dribbles and hit a 12-footer over Hibbert's outstretched arm as time expired, giving Miami a 56-46 lead at the break.
Miami missed its first shot of the second half, then didn't miss another field-goal attempt for eight minutes.
Seven straight makes by Miami fueled what became a 21-7 run, and essentially took away any mystery about the outcome. What was an eight-point game turned into a 77-55 Heat lead, the margin exactly doubling the biggest leads Miami held over Indiana in the first two meetings between the clubs this season - combined.
From there, yes, there were reminders that these teams aren't exactly fond of one another.
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Stephenson, who made a choke sign at the Heat during last year's playoffs, then was the subject of a flagrant foul from now-former Heat backup Dexter Pittman later in that series, drove the lane with 3:05 left in the third period and drew a hard foul from Battier. Stephenson remained down for a few moments, and a video review confirmed that Battier made a play on the ball, so anything beyond a common shooting foul wasn't merited.
It might have fired up Indiana a bit as the Pacers scored the final nine points of the third quarter to get within 79-65.
They could have gotten two more points closer if not for a brilliant defensive play by James in the final seconds. George got free for a layup, but James stalked him on the break and swatted away the shot.
NOTES: The 18 straight wins ties for the second-best streak by a reigning NBA champion. Boston won 19 straight in the season after the 2008 title, and the Celtics won 18 in a row after claiming the 1981 championship. ... Chalmers scored 11 points in the first quarter alone, topping his 7.9-per-game season average coming in. ... Pacers coach Frank Vogel picked up a technical early in the fourth quarter.