A very easy way to do it would just be to serve the ball at > 400km/h. It's unlikely that a human could accurately return a ball at that speed more than 50% of the time.
I don’t know the rules of tennis well enough, but would it be enough to just have an unreturnable serve to win, even if you can’t return anything yourself?
no, you have to win by two games. So you have to be able to win once with your opponent serving.