Have you ever noticed that when the match gets tight, your serve does too? After throwing in bombs during the early going, you find yourself struggling to get the same stick on the ball. Join the club. During the difficult moments of competition—break point down, for example—it’s normal to become tense. And when you do, it’s common for this tension to manifest itself in your serving arm. The fluid and relaxed feeling you usually have in your arm, a condition that’s necessary to deliver a potent serve, is instead replaced by unintentionally-flexed muscles and a death-lock grip, both of which affect the swing on your serve.
To combat this, take a couple of seconds before you serve on important points and make a conscious effort to relax your hitting arm. Take a few deep breaths and shake your arm to loosen it up. This will help you keep your swing smooth, which will, in turn, enable you to serve well when the pressure is on.