Easy Wins In Career Mode:

Go to the options menu and set Illegal Blows to Off. Then, go to the fight store and buy the illegal head punch called Elbow Shot. During a fight, use the Elbow Shot to counter attack each time your opponent throws a punch. Note: Make sure you use the Elbow Shot as a counter attack so that you can connect cleanly and powerfully on you opponent's head. You will see that the Elbow Shot inflicts a lot of damage to your opponent, and will KO him in a short period of time, or TKO because you inflicted so much damage to his eyes.