I know I'm kinda of stating the obvious here, but game 3 is crucial, especially for San Antonio.
I know Miami won game 3 at Dallas back 2011 and Dallas still won the series by reeling off 3 straight, but I don't think San Antonio can do the same. Miami still isn't the best team under pressure. The respond with their backs to the wall, but only in spurts. If San Antonio can win game 3, they can keep the pressure on Miami's role players to perform, and those role players have been very inconsistent in these playoffs.
If San Antonio keeps the pressure on with a game 3 victory, then I think they'll go back to Miami up 3-2. But if Miami wins game 3? I see them closing out the series in game 6 at Miami.
If the Heat role players continue to play as they did last night, then the Spurs are pretty much just waiting for the inevitable finals loss.