Best done with 2 controllers, as you wont have to worry about your opponent scoring and you can keep knocking them down for power-ups.
The power-up for this is a green +2. After obtaining this power up you will need to score 2 goals with the player its attached to, it does NOT have to be the same player.
Also you will need to attain this power up at least twice, as it disappears after you make the goal.
This also must be done during a single game, it isn't cumulutive, just make a game to 20 wins and concentrate on taking out each one at a time.