Fight Night Round 4

This method will work for all the Fight Now achievements.

After picking boxer and opponent go to setting screen and set the required difficulty. Change rounds to 1 minute and fight length to 1 round. Adjust sliders in your favor and cpu sliders down. When fight starts get a flurry of punches on your opponent then run away. You will win by decision and achievement unlocked.

There's a trick here that I haven't actually found anywhere else.

When you're adjusting the sliders, move Boxer Power up, but move Boxer Toughness *DOWN*. This was completely counterintuitive to me, but it made all the difference since it affects both you and your opponent.

Against Ali, make sure that your boxer is about 6' 4" with a very long reach, so that you stack up well physically.

Set your round to a minute and the length to one round. G.O.A.T. difficulty, as specified in the achievement.

Go straight after him at the bell. Throw hooks to the head and as many punches as you can as fast as you can. With some luck, you should be able to knock his health down quickly and possibly knock him down. If you can do that, then retreat for the rest of the round with your block up and you should win by decision.

But make sure that Toughness slider is down. That helped me go from getting knocked down repeatedly to winning the fight in one game.