Rocky Balboa right at the end of Rocky 2.
Anderson Silva as he is now.
Round one: Streetfight, no rules, they're both mildly enraged, fistfighting it out in the rainy streets of Chicago. Nobody else interferes or is even around. Start 50 feet apart.
Round two: Boxing match, for the title of "overall world champion", since they're technically in different weight categories.
Round three: MMA match, for the title of "overall world champion" again.
Who takes majority?
Win by KO in all three matches.