(Same guide as Story Mode+)
The other guide is great if you want to grind and get this legit but...
I started a quick match with 4 controllers. I set the score to 11 and won 11-0 with my main account. I then went back to the main menu and went to story mode and then continue. All the players will be lined up on one side. Just use Y on your second team to miss the serve and then continue to press the X button with your main team until you win the game. Should take all of 10 minutes to get these two achievements. Please let me know if you have any issues or questions.