It was a total team effort from Miami, and they needed it with LeBron James (17 points) not at his explosive best. Four other Heat players stepped up to reach double figures - Mario Chalmers top scoring with 19.
San Antonio's 'Big Three' of Tony Parker, Manu Ginobili and Tim Duncan combined were just 10 for 33, with Duncan's 3-13 shooting his worst in an NBA Finals game.
"They outplayed us," said Duncan, "We didn't play well, we didn't shoot well and I know I played awfully."
After a first half that mirrored the tight nature of Game One, with San Antonio's Danny Green scoring four of four three-pointers, Miami broke away in the third and headed into the final quarter with a 75-65 lead.
League MVP James was strangely ineffective on offensive, however, managing just eight points on three of 13 shooting through three quarters and missing a couple of routine lay-ups.
However, he came alive late in the third and carried a more aggressive approach through the fourth as Miami finally produced the offensive power that was the hallmark of their form until the Finals.
"When I was struggling offensively, my team mates continued to keep it in range and we even had the lead," said James.
"I think Rio (Chalmers) more than anybody kept us aggressive ... it allowed me to sit back and wait for my time," he added.
Miami's devastating 33-5 run put the game well beyond San Antonio, whose coach Gregg Popovich opted to play the final portion of the fourth quarter with reserves on the court.
Ray Allen and Mike Miller each chipped in a trio of three pointers for the Heat while Chris Andersen went three of three shooting for nine points.
James, who like Miami's other starters also sat out the latter minutes, finished with 17 points, eight rebounds and seven assists but before taking his rest, he brought the crowd to their feet with a stunning block on a Tiago Splitter dunk.
San Antonio's Game One standout Tony Parker was handled superbly by Chalmers and limited to 13 points on 5-14 shooting.
After committing only four turnovers in Game One, the Spurs gave up 16 on Sunday. Parker, who was without a single turnover on Thursday, conceded five.
Spurs head coach Popovich said there was no question of fatigue and no excuses for his team's performance.
"Miami did a hell of a job. Nobody is tired, we had two days off, there's no excuse. The season does get long for both teams but they would both rather be here than at home.
"So it's not about tired. It's about Miami played their ass off," he added.
Game Three is on Tuesday in San Antonio, the first of three games in Texas before the series returns - if needed - to Miami for the final two games.
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- Mario Chalmers
- San Antonio
- Tony Parker
- LeBron James
- Tim Duncan