In tennis, if I kept winning a point. I would only use that ball until I lost. Even if I had two balls I would insist they give me the ball I won with.
The informant uses this superstition when she is playing tennis. She played competitively in high school but she also utilizes this superstition when she plays for fun. She said uses the same ball because it must be special if she keeps winning.
I personally do not believe this superstition to be true. I do not see how the same ball could keep you winning. However, the use of one ball may keep the informant focused on winning and thus she will continue to win the point.