The Italian fired a passing shot howling by his Bulgarian opponent for a crucial break in the first set and captured the opener with a brilliant backhand winner that brought the fans at Hard Rock Stadium to their feet.
Dimitrov, who has experienced a career renaissance this season, had no answer for Sinner's flawless game in the second set and was broken again when his backhand landed in the net to fall behind 3-1.
Dimitrov badly missed an overhead to hand Sinner the 5-1 lead in the second set and did not even try to chase down Sinner's backhand winner on championship point.
Australian Open champion Sinner, who scooped a second Masters 1000 title following his success in Canada last year, will rise to second in the rankings for the first time.
