Virtua Tennis 4

Quite easy achievement.

Can only be won during world tour.

You don't have to gain all 3 partners in one world tour as you will keep the partners over the playthroughs as the 3 accumalates over your game play.

Your starting partner Theron Tenniel doesn't count towards your three as you have to unlock three new players as the three i unlocked were Roddick, Gonzalez and Seppi but you may come across different partners in your game.

To earn a new partner you will receive a message on your screen while playing through your world tour stating they'd like to become your new partner but you need to prove yourself first.

So once you've gotten that message to unlock them you need to participate in a VS training session which are:
Wind match
Bomb match
Wall match
Coin match

The reason why only them is because you will play off against that player so you need to get the required score for the training session and then he will be accepted as a new doubles partner.

Stick to low level trainings as you don't want to have to be trying to unlock them on level 5 or 6 training sessions because if you fail you will lose out on him until next time your approached.

If your unsure how many partners you've unlocked you can either go to your club on your world tour and look under doubles partners, or on the main screen go to my club and click on medals and on page 5/10 it will tell you your stats towards the achievement.