In the options (press Select) set number of rounds to 1 and when selecting opponent set AI difficulty to 'Very Easy' (can also use a second controller if available).
Hit the enemy until their health bar is drained at which point 'FINISH HIM' will appear on screen. Position your character in the appropriate spot and input the following commands:
Split Decision (Mid) - Back, Forward, Back, Forward, B
Double Trouble (Close) - Down, Down, Down, X
Then when the points are tallied hit 'Retry' to restart and perform the second finishing move.