Instead of attempting to hit the tying basket on the buzzer leaving Miami no time to win it in regulation, Durant went up immediately. He ends up missing, and even if he makes it Miami still would've had the ball with 9 seconds left.
Always take the early shot if you're losing, trying to take a shot on the buzzer if you're already down isn't the correct play. The early shot gives you a chance at grabbing an offensive rebound if you miss, plus you have the chance to foul and extend the game, if needed. Running the clock down essentially gives you one chance to make a shot, or it's game over.
If you make the early shot, be glad you've tied the game (or taken the lead with a 3) and go and play defence to seal the win.