Create a Boxer and make his Power 100 and toughness 100. Go to "Fight Now" and press to edit the settings. Change difficulty to G.O.A.T. and number of rounds to 1. Change the round length to 1 minute and change the Boxer settings so they are all the way up and CPU settings so they are low.
Tip: Mike Tyson has a very strong punch and will attack you. If you try to punch and move back, he will stay on you. A good way to start is to throw a a haymaker so he will step back a little. Also throwing right hand straights as well as moving back to avoid being hit.