I think Miami comes out strong but after that initial wave of adrenaline wears off I think the Spurs slowly take control and wear them out with their superior ball movement.
I expect LeBron to have a huge game but I don't see anyone else on the Heat stepping up to give him the help necessary to beat the Spurs.
The Heat are the older team and it shows. They take entirely too many plays off, especially on the defensive end. The Spurs will run them ragged with all their movement and by the late 3rd quarter I expect the Spurs to be in full control.
And if by chance the Heat play balls out and actually win tonight, with the short turnaround and having to play again on Tuesday night, I don't think they'll recover enough to play elite basketball in back to back games.