It seems to me that most of the time, the player that has the better control of the ball wins the match.
Not always, but that person has a leg up on his or her opponent. I have found that sometimes when I am warming up for a match that the handle feels too large when I grip it. When the racket seems to drag through your swing, you have got a problem.
To take care of that feeling, I use an old grip that I have taken off another racquet and wrap it over a racket that is the same size, etc., as the one I will be using in the match.
I then hit with this oversized grip for two to three minutes in the pre-warm-up or the actual warm-up.
When I go to my regular racquet for the rest of the warm-up, it gives me a great feel because the handle itself seems smaller. A mind game yes, but effective.
Note: Smaller grip size means more control, and unfortunately less power. Make the choice.