Kessler's defense against Soliman in the sparring tape looked ordinary, but he took Mundine's jab (terrific jab) away for large portions of the fight and blocked most of Mundine's flurries (handspeed comparable to Calzaghe). He also beat Soliman up quite badly in hard sparring before the Mundine fight.

His defense seems to be based on blocking with his guard rather than slipping but this seems common among a lot of European guys. I think he backed away with low hands against Mundine and Siaca because they were being controlled and were timid about coming after him. Mundine is a safety first fighter who won't open up until he establishes his confidence while Siaca was flat out getting the snot beaten out of him.

I think Calzazghe will beat him but not because he's weak defensively, rather that Joe is much quicker on his feet, throws a lot more leather and is a southpaw which will mess with his jab (which everything seems to start with for Kess)