Aqua, you've taken the words out of my mouth. I couldn't agree with you more.
That said, I think too many people have reported experiencing this "cpu boost" for it to be imagined. If you are a PES god and therefore able to hold the cpu opponent off and win, then more power to you, but frankly I don't care what you have to say when you start your post off by taking cheap and immature shots at people. What I do care about is bringing up matters like this one and discussing them so that the NEXT pes/we is even more realistic. Every version of PES has been better than the previous. PES4 excells in so many areas that PES3 did not, but that does not mean it cannot be improved upon. It is important that gameplay issues such as this one, are brought up and discussed so that our friends at Konami might take notice and improve upon them in future releases/patches.
Perhaps it is a matter of stamina, but I cannot tell you how many times I have brought in fresh defenders and swapped to a defensive formation only to still have this happen. (And yes, I've also tried to keep my formation, as I have also tried to be more attack minded, it matters not.)
Just because someone raises a question and voices an opinion doesn't mean they do not enjoy playing the game.
I'll ask you the reader to put your pride away for just a minute and be honest. Those of you that report being able to hold off the cpu and complete the win without a problem: what difficulty are you playing on? Even if you do not experience a drop in your own players performance, do you find the cpu stepping up their own efforts? Do you find league play more challenging than "match" play?
EDIT: The two posts above this one came in as I was typing. Perhaps it is a game length sensitive issue. I have been playing 20 min matches in ML.