Hi there, your mate is what we call a cut-back whore to be exact. It's not particularly an appreciated tactic he is using as he is taking advantage of a fundamental flaw in the game which sees the goalkeeper mispositioning himself during the cut-back pass into the 6 yard area or further out.
Being a longtime PES fan yourself, you probably already know that this cut-back flaw has been unfortunately available since around PES6 I believe. I used to play in an online league myself, however we frowned upon the use of the tactic and often made a conscious effort not to score such goals as they were effectively considered 'cheap'.
As for how to counter this tactic that your friend utilises, it's a tricky one, but it can be countered (for the most part) through practice. This includes using the pressure button when defending (X for Xbox 360, Square for PS3 of course). By using the pressure button to defend, it will move your closest player to the ball towards your opponent who's in possession in an attempt to put pressure on him through either tackling or jockeying. This pressure of course is applied without you even controlling the man meaning you effectively have a free man to control, which is the key here to defending the cut-back tactic. You can use this free man who's fully under your control to either double up on the winger who's preparing to make the cheap cut-back, or you can alternatively use the free player to back off and fill in the space within the box where your opponents winger is likely to pass the ball, ultimately intercepting the cut-backs.
In terms of formations, I probably couldn't help you out with that one, but I wouldn't advise playing 3 at the back, and stay with at least 4 in defence. I often utilise the counter attack strategy too which tends to work very well, especially if my opponent is committing many men forward which I imagine your friend does if he indeed plays the 4-3-3 formation.
As I say though, the key to stopping the cut-back tactic is mainly in the pressure button I believe, and it's a matter of practice. You've been playing a while mind (I started with ISS 98 too! High five!), so I imagine you can adapt quite quickly. You just need to really use your own judgement in the moment as to whether to double up or use the free man in your control to fill in the space and intercept the pass. The only other thing you then need to be wary of is overusing the pressure button and the location of using it, as the AI when under the control of the pressure button are known on occasion to slide and give away fouls which isn't particularly helpful in the box. So just maybe ease up on using the pressure button once the winger is in the box, but it is a judgement call of course, and in the moment you're the best judge.
Hopefully this has helped, and to repeat, it'll probably take a few matches to really get to grips with this defending tactic if you're not trying to implement it already.
Oh, and just a little word, we don't really condone swearing in thread titles so just keep that in mind for next time - and try to refrain from double posting. We don't mind double posting if it's a few hours apart or so, but not a few minutes. But you're new here so it's only right to cut you some slack brother.
Anymore thoughts or advice, just post back, there's plenty who'll be happy to help. And good luck beating him, he deserves to lose.
