This has been a tried and tested method that has worked in recent years for PES games.
Basically, if you go to the Edit option on the Extras menu, you can edit the ability of individual players. For the Asian Treble Winners achievement, you can select any team playing in the AFC Champions League and they will also play in the Asian League. When you're editing players, hold down the X button and press right on the D pad and it changes ability 10 at a time. You only need to edit the starting 11 and a handful of extra players.
By making your team perfect you'll be able to simulate every match (select "Skip match" instead of "Next match") and win every competition you're in. Save regularly in case of unexpected results (I won 100% of my matches first time). You'll also be showered with a lot of GP to help improve your myClub team too.
A cheap way to victory but I don't fancy playing through several entire Master League campaigns.