The Heat surprised many by progressing to their sixth appearance in the finals, securing their berth with a 125-113 defeat of the Celtics on Sunday.
Bam Adebayo led the way with a season-high 32 points, as well as 14 rebounds.
Jimmy Butler scored 22 points, while Tyler Herro had 19.
The game was tight at 88-86 to Miami at three-quarter time, and Boston took a six-point lead early in the fourth.
But the Heat lifted to power past Boston in the home stretch, ultimately dominating the last quarter 37-27.
The Celtics, who lost the Eastern Conference final for the third time in four years, were led by Jaylen Brown with 26 points and eight rebounds, while Jayson Tatum had 24 points and Marcus Smart and Kemba Walker 20 each.
"This group, more than anything, they just love to compete," Heat coach Erik Spoelstra said after the game.
The Heat are now the only team who can boast six final appearances in the past 15 years, while the Lakers are in the decider for the first time in a decade.
Game one of the seven-game final series is on Wednesday night.