The Spurs led 75-65 after three quarters, but there were some wild spurts.
The Heat closed to within 57-56 in the middle of the quarter, but the Spurs responded with an 11-0 run.
San Antonio led 71-58, its largest advantage of the game, before Miami put together a mini streak of five straight points. But James and Wade missed layups on successive possessions -- both were begging for foul calls -- and Parker and Gary Neal hit runners on the other end to kill the Heat's momentum.
The Spurs closed the first half on a 17-4 run to take a 50-44 lead into intermission. Duncan had 25 first-half points on 11-of-13 shooting. It was his biggest first half since 2006.
Meanwhile, James had just nine points on 3-of-9 shooting before halftime, although he did have five assists. James went 0-for-4 against Boris Diaw.
NOTES: The Spurs and Heat went with their same starting lineups from Game 5. ... In a knee-on-knee collision, Wade was called for charging into Ginobili in the first quarter. Wade came away limping but stayed in the game. ... Heat F Chris "Birdman" Andersen, who was not used in the two previous games, entered Tuesday with 1:41 left in the first quarter. He made an impact -- literally -- in the second quarter, diving into the second row to save a ball. Andersen wound up with one point in 14 minutes. ... Leonard gave the Heat's Mike Miller a "facial" in the first quarter, dunking on the Heat wing while hitting him in the face with his off hand.