I doubt Kessler underestimated him. He just flat out got his ass handed to him. Calzaghe showed Kessler's fatal flaw: The inability to adjust. Ward exploited it even better than Calzaghe. This was really a clear case of superior fighter on may levels. Speed, accuracy, defense and movement.
Underestimated him - proberbly - his trainer did for sure. But I don't think that's the main problem. I think it's a combination of ringrust, the strain of the legal battle with Palle and the enormous pressure he has been under as the favourite. Look at his smile after the fight, when he says something like "now I'm not the favourite anymore - I don't want to be the favourite" - it's a smile of relief. I think Kessler snapped under the combined pressure of rust, legal deisputes, being the favourite and the away factor.
Yep. I think he underestimated Ward and prepared very very poorly. First off, you never underestimate an Olympic gold medallist. Secondly, it is a well known fact that Ward switch hits. None of Kessler's sparring partners were southpaws. . .horrible preparation. Kessler looked like a fool when Ward switched.