is it the game engine work too logic?

[Mr Mercury]

Your english is awful, sorry to say. But you mention a 20% possession on your side so i guess you used an illegal formation, hence the cathastrophic result.

His English is not the best but it's easier to understand than some on these forums. He said 20% above, so I read that as 60-40 to the home side.
But a 4-0 result in those circumstances is not unusual, the level difference wouldn't even be a factor, just better formation and tactics.
For the return leg, I'd go attacking with something like 3-4-1-2.