I've been playing Wii tennis off and on the past couple of weeks, totalling probably around 10 hours. I've found a pretty consistent way to beat the top players (Elisa at 2000 and Sarah at 1900). Here are a few things to keep in mind (at least that's the approach for me anyway):
1. You'll win over 95% of your points with your net player, not your baseline player. Your baseline player though will be important in setting up the point so that your net player can hit the winner.
2. Use your baseline player to control the ball and make the computer's baseline player move back and forth consistently. To do this, you'll need to learn to control the ball and use various techniques such as heavy top spin cross court shots to push the other player out of the court. The side slice can be done consistently, but it doesn't do much tired the computer opponents. Heavy top spin is better way.
3. It will seem that the computer opponents will get everything back, after all Elisa is rated at 2000. However, keep up the pace and you'll see both computer opponents begin to sweat. This is when they'll slow down and start missing some shots and won't run as fast.
4. Don't be too anxious to hit a winner. Make the computer opponents work before trying the winner with your net player.
I use the approach above and can consistently beat Elisa and Sarah 3 out of 4 times. Once a while, I would have a bad game by being too anxious to put away points and hit the balls out. The technique used here is actually quite similar to playing doubles tennis in real life. In most cases, your baseline player has to set up the point for your net player to win. One difference though is that I can't make both my players go to the net in Wii like I would in real life. Oh well.
At this time, I'm rated at 1900+. If I have more time, I will try to pass 2000. It seems though that Elisa and Sarah are the final computer opponents since they are all that I play against. Perhaps once I've passed 2000 I'll see someone new.
BTW, does anyone know how to hit a power overhead? It sucks that when the computer opponents throws a short lob and I canít put it away with a power smash. I can angle the volley fine, but it would be fun to smash the ball right at the computer opponents.
Have fun at tennis!