"David and Goliath" and "King of the Rope-a-Dope" achievement hints
Set the round time to 1 minute and up to only round 1. Simply punch him enough to win by decision. This may also work for the "My Style Is Impetuous" trophy. Do the same while fighting Mike Tyson, but with a created boxer.
Set the rounds to 2 minutes and select someone like Foreman. Continue blocking and punching. If done correctly, you should knock them down and get the achievement after the fight.