Bob,
I think it has been discussed a lot that replaying a game is not really a fair test. I don't mean cheating. Think about this in terms of the game code and real life as well. In terms of the code, there is some randomness (it muust be). Roughly speaking, the outcome of the game is probabilistic, though if you choose right players and right tactic, the probability to win increases. It is much higher if in addition your squad is far better. In real life it means the following. Two teams play against each other, and one of the teams (say you) focus on attacking, while the other is looking for counter-attack opportunity. If you score first, then the other team game plan needs to be adjusted since they have to respond. If you don't score early, your players became nervous and start making mistakes. Of course, the game code do not have emotions, but it tries to model real life with more or less success.
Your example with winger, who turned game around may mean 2 things. Either he is a player who is better against a particular opponent, or you just ruined the other team plan by scoring first and they couldn't find a way to change it properly. Same thing with mentality change.
I used to play semi-proffessional, and still cannot explain why one day almost every shot I made was a goal, while next game I could miss empty net from 6 meters with no pressure three times in a row

And you are looking for explanation of something much more random.