This can be done on the first fight in Arcade Mode.
Set the difficulty level to Very Easy and then set the round limit to one round only. Then chose your favorite character and enter the first match. It doesn't matter if you get hit, but not to the point of where you'll lose the match. So all you have to do is pummel your opponent until he or she goes down for the count. The achievement is yours once you won the fight and your character does his or her victory pose; it unlocks through all that.
Have fun and good luck! If you feel like submitting a negative vote instead of a positive vote, please tell me why and I'll happily correct it to make amends on my behalf for my solution. Thank you!