Very easy, on the main menu :
2) Custom Tournament
3) Difficulty (expert), match type (single), rounds (3), sets per match (1), games per set (3), final set (tie break)
4) Press A, now you should be on the character selection screen, pick who you want but Federer is the GOAT
5) Tournament venue selection don't matter press A until you get to proceed
6) You should be on a page where you see the two players, and Quarter Final written on top. Plug a second controller, Press Y, and select an account or a guest.
Press again Y, it should show you the red controller, pick the other player side. Well you won't be able to select the same side as your main anyway.
7) In the match, make your main account win.
8) Do this for the two other matches, shouldn't take more than 1 min a match, since it's 3 games.
9) When you win all 3 matches your main will unlock the achievement.
If something is not clear, complain in the comment section and Ill fix it. Have a nice day everyone.