Update: Choose Lee first because you fight Mickey after him.
I found this achievement easy to get using the character Mr. Big.
Choosing my opponent Mickey because I find him one of the easiest characters to defeat.
This link will show how I was able to beat the first opponent repetitively using the same special attack, getting 2 perfects and earning almost 120k in the first fight.
The special attack is made by going down on the left stick and moving towards the right (forward) then tapping A.
Keeping the motion going isn't easy to start with but gets easier as you practice it.
So as soon as you fire the first special attack, you want to keep the left stick in a motion of going from down towards right and back with your thumb whilst tapping A.
"What I've done just turn the left analog stick against the clockwise cn_LS_cn_LSc all the time and press cn_A sometimes you jump over the enemy. Then simply in the other direction. Pick Mr. Big against Lee... on second fight Micky you must do a perfect but thats easy to do...
At the third opponent you have your points or earlier" - @CLARION 85
The only problem of picking Micky first is going agaisnt the ninja character after. It's not so easy using the same method to defeat him since he can find a way round to attack you but winning 1 round agaisnt him should be enough to earn 120k. I still defeated him but that was by mixing in different attacks and blocking.
Good luck.