It is realistic, no doubt, but it has its moments.
I thought I was going crazy when I noticed a few teams beating me with not long to go, with some ridiculous shots from nowhere that somehow went in, but Drekkard assured me that the game just doesn't let you win on occasion. Not all of the time - not very often at all in-fact - but sometimes.
I suppose we just have to get used to the fact that, with processors the way they are at the moment, it's not possible to have 21 AI players (that's minus the one you're controlling when you play 1vCPU) behaving in a realistic way and getting a realistic scoreline by playing "fair".
(And I suppose the proof of that is that you get less of these incidents when you play sports games that involve less people.)