I think Gatti gets busted up from the kinds of shots Mayweather throws. RSC sometime during the 2nd half of the bout.
Mayweather has a big edge in reach and skills (and could whack himself). Gatti has the better chin, very good power and a heart that wouldn't quit no matter what obstacles he faced. I could see a facsimile of the Wilson fight with the taller, rangier Mayweather out landing, out boxing and busting up Gatti early. But Gatti would roar back at some point and the question is how would Uncle Roger cope with this? The head says that Mayweather had enough tricks and smarts to survive some shaky moments and reestablish control and eventually stop Arturo on cuts or swelling. The heart says that Gatti is a huge chance to rally from behind and take Mayweather out mid rounds. Great match up for sure.