MIAMI - Amazingly, the tombstone of the Heat was being chiseled 17 days ago when they dropped a 94-90 decision to the Celtics at home in Game 5 of the Eastern Conference semifinals, and were one loss from elimination.

And the reputation of LeBron James as a wunderkind unable to propel his team to greatness was no longer an unfair assessment. It was reality.

But on Thursday night at AmericanAirlines Arena, the Heat broke the hearts of those traditionalists who did not want such a team compiled through free agent dollars and the lure of a sexy city to win a championship. And James broke the hearts of those who wished him nothing but playoff failures after leaving the Cavaliers in such a controversial and publicized fashion.

The Heat are NBA champions, primarily because of the heroics of James, who scored 45 points in Game 6 against the Celtics, and then catapulted his team to an impressive title run that culminated with a 121-106 win over the Oklahoma City Thunder in Game 5 of the Finals.

Miami won the series, four games to one, pummeling Oklahoma City in the second half, helped by the 3-point shooting of unheralded Mike Miller. James finished his masterful run with a triple-double and Miller canned seven 3-pointers to finish off the overwhelmed Thunder.

After a series of postseason failures, his much-criticized free agent decision and playing into a villain role last season, James appeared to reassess his approach and emerged as the Heat’s leader, avoiding the late-game failures that plagued him during last year’s Finals. James, who was named MVP of the Finals, was considered one of the game’s greatest players never to win a title, and it took nine years to erase that tag.

James left the game with 3:01 remaining, looking to embrace anyone within arms’ distance. He then ripped off his headband, hugged assistant coach Bob McAdoo, who was a prolific player who did not win an NBA title until his 10th season.