Andy let Muller win because Muller is a good guy so Andy was being generous as he usually is. Also, he knows that if he loses early Blake and Ginepri would shine and that would do their careers and that he wouldn't have to beat Agassi so that Agassi could have another moment in the sun. Andy is that kind of guy.
Clearly, if Andy wanted to he would have won basically every match but he thinks the world of Federer so he's letting him win and of course Safin and Nadal are good guys also so he's letting then win and take the spotlight. It is all part of his masterplan.
I have hit with him in secret and he has a first serve that he can consistently hit in either corners at 160mph + but he feels that it would hurt tennis because it would also be boring, with him clearly the dominant player. His two handed backhand is weak but that is because his real backhand with his right hand is a one handed backhand. The one handed backhand is better than fed/gasquet/guga combined. His volleys are better than Edberg/Becker/Mac/Sampras/Rafter put together but as you can see it just wouldn't be fair. Andy also has been doing wind sprints, his best is a 9.5 sec in the 100 meters, world record beater but that would make the sprinters feel bad so he's keeping it a secret. Likewise, he can run the mile under 3 minutes and do the marathon under 2 hours. Andy is also the only guy to have beaten Lance in the secret US Biking proving grounds. In addition, he's been practicing with the Bolshoi Ballet and beating LeBron James/Shaq in 1 vs 2 pick up games.
So to all Andy fans, do not fear, your hero is an incredible athlete but more importantly a generous human being, his moment will come but he does not want to be just another American champion,he wants the other countries to have confidence in their program and to promote tennis as a global sport.
As his secret hitting partner, I believe that when he is 30 or 35 yrs old, Andy will reveal his true capabilities, by that age, his skills will be diminished and the younger players will have a better chance against him.
BTW, you do know that Andy is really left handed and that his right handed game is just for fun?
