The last time (only time) Jirov fought at heavyweight he was around 200 lbs. Mesi usually weighs over 230. If Jirov's plan is to stand right in front of Mesi and trade shots like he usually does, his good chin won't matter. I seriously dought Jirov will ko Mesi giving up that much weight and Mesi seems to have a pretty good chin, but Jirov will definitly throw and probably land more punches. This fight will come down to how many heavyweight right hands Jirov can take giving up +/- 30 pounds to a guy that can definitly punch hard. Personally I think Mesi will ko him in the mid to late rounds.