The only reason he won is because he knew how hot tempered his former Padawan was. He used his superior experience and his knowledge to his advantage. Anakin was also well versed in Soresu, he just favored Djem-So more. If you know the history of Djem-So, you would know that it was developed by Soresu practitioners who wanted to add offense. They married Soresu's defense with Makashi's aggressive style. So the solid defense was not what won him the fight. Anakin had a solid defense as well.
The fight could have gone either way until Obi-Wan goaded Anakin into making that near fatal mistake. Neither one had a clear advantage over the other. They seemed to be evenly matched in nearly every way up to that point when Obi-Wan capitalized on Anakin's belief that he should be the more powerful and therefore able to overtake any perceived advantage Obi-Wan had.
The problem of Anakin is that he was full of anger and hate, but as a Jedi he never took the training of how to control and direct these emotions.