Have you listened to Zimmerman's conversation with the Police dispatcher?
It seems to be the whole thing, I listened to the version directly from the Police Department. Zimmerman was still in his vehicle when he reported, "He's running", then he got got out and attempted to keep Martin in sight. The only time Zimmerman sounds at all "charged up" is right after that report, and before he got out of the car, or possibly as he was getting out, ".. the **** always get away". Then you can hear that Zimmerman is moving, and so can the dispatcher, who then asks, "are you following him?" Zimmerman says "yes", the dispatcher says "we don't need you to do that", Zimmerman says "OK, and pretty much right after that, you can tell that Zimmerman has slowed down (breathing mostly), but is still outside (wind noise). He then discusses with the dispatcher where he the police should meet him. Doesn't sound like someone "looking for a fight".
I don't know that Martin was looking for a fight either, but it certainly sounds like he circled back, completely possible given the layout of the buildings in the complex, and attacked Zimmerman. He could have just as easily, once he'd broken contact, have gone to his father's girlfriend's place, which was not all that far away, in the opposite direction from where Zimmerman had said his vehicle was parked.