I think the theory works completely here. In the beginning of the fight it takes less than a minute for Obi-Wan to...un hand him (classic). Seriously though he takes off two hands and force blasts him really far. At this point a battle rages and he loses some of that balance over the force that he had. This was a complete victory and Obi-Wan even saw it in the beginning. He even smiles when he sees it.

When he gets kicked he un arms him beats him down and goes into a killing blow (perhaps he saw this would be it) but since half of his body is robotic couldn't forsee him having such a huge kick. This is going to throw anybodies focus off and screws him up for the rest of the fight.

Compare this to the Count Dooku fight where he was completely unmatched as far as using the force and lost immediately. It also explains how Anakin is able to hold his own even though he is far less experienced a Jedi as Count Dooku is.

I hate to ramble here but think of the first fight between Luke and Darth Vader. Luke should have been able to beet him. He is younger, faster and not half robot. But he gets completely toyed with because even though he is better with the blade (which is what he was using it as) he is worse with the force. He is not able to read the movements or dodge at all.