Actually, being the "Master of Soresu" had very little to do with the win. Obi-Wan goaded him and Anakin fell for it, literally. He did exactly what Obi-Wan expected him to do and Obi-Wan capitalized. It came down to which one was able to keep their head in the game.
Except if Obi-Wan wasn't the master of defense, he would have more then likely be beaten. Goading someone isn't a good thing to do. The only reason Obi-Wan won, was because he had a solid defense.