Kimbo "lost" due to an illegal blow at 0:07 (clubbing blow to the back of the head)
http://www.youtube.com/watch?v=qekdLpSXOfc&feature=relatedThe initial punch thrown by Petruzelli was inconsequential - he was standing on one leg, leaning backwards, and did, what is called in boxing, an "arm punch". Because the rest of the body is not behind it, arm punches have near zero power, and are certainly not capable of knocking anyone out.
Now Kimbo did throw himself into the arm punch somewhat, but I do not believe that it was a knockout blow because he held himself up quite well on all fours when he went down (he clearly was not out).
What took him out of the fight was the big chop to the back of the head at 0:07 when he was completely vulnerable, down on all fours - I checked the rules of this organization, and that was a flagrant foul.
In short the fight was a fluke loss - caused by an ignored foul.
Not a fan of MMA stuff (old time boxing fan - no longer) - saw the link here - watched the videos - I really don't care for the sport or either fighter... just saying.