Personally, I think it just takes practice for your reflexes after playing it a lot (and some luck). If the AI has already won 2 matches within the first 10 or so seconds because you weren't prepared, it's unlikely that you will be able to win 3 matches without making a single mistake so just restart at that point ^^ Also, faster speeds are easier to win against the AI than slower speeds.
Try to hit the ball near the corner of the paddel. It will make the ball careen at an agle at a faster speed. The AI is too slow to respond to fast balls at an angle.