Go to single-player, then choose CPU Battle. You must defeat all 8 enemies there. To defeat an enemy, beat him twice (best out of three). If you want to make it easier on yourself, go to Settings and put the game on Easy; you'll still get your achievement.
ps: make sure to finish this in on sitting; if you quit and try to restart, you'll have to start at the beginning. This achievement took me around 16 minutes.