Most likely, your 90+ mph first serves are hit very flat. Therefore, you are probably missing them more than half the time. Hitting all those faults will destroy your rhythm, so when the ball actually does come back, you're not ready for it. My suggestion is to hit the first serve with spin, so you can get more of them in and get in a better rhythm for the actual point.
Last edited by Topspin Shot; 10-13-2013 at 05:55 PM.