With the speed and power game prominent in a modern tennis match, players are often caught off guard when the ball is hit short. A couple of basic ideas will help you handle this type of situation:
Turn your shoulders prior to running in and remind yourself to use a short backswing on this ball. Once you get to the ball, slow your feet down and make a smooth, normal, forward swing with your regular follow through. The tendency is to swing quickly with a big backswing and a short follow through which tends to result in the ball flying off the racquet, or a mishit shot. The swing with a shorter backswing and regular follow through will produce some rotation on the ball (slight topspin) and keep your shot deep and under control.
In addition, because you are using something close to your normal swing, it is more likely you will hit the ball solid and time the swing well.
These two things will give you the confidence to react quickly and decisively to the short ball, and help make you feel like that there is more time to execute your shot.