City were comfortable 3-0 derby winners.
"You have to look at what we did well," said Fernandes to manutd.com. "It was obviously not enough because you want to win football games, not see the positives from the game. What we did here was not enough to get the result. All we have to got to take from this game is obviously to look at what we need to do better and go forward to the next game.
"We need to score goals and not to concede. It is the main thing of football. We keep creating chances to score and we are not able to score as many as we wanted. We have to be more in control of certain situations. We conceded three goals that should have been avoided. For the first one (by Phil Foden), we need to be more brave. When we go in full pressure in one-v-ones, City take that risk against us today. We need to do the same.
"The second goal was from a throw-in and we need to be much more aware in that moment. The third goal, a thing like that can happen, but we need to be in a better position to not being countered like that."
Asked if maager Ruben Amorim's system is the problem, Fernandes insists it's up to the players to make it work.
He continued: "We play with a back five, sometimes a back four or three, whatever you want to call it. We need people to be very aggressive in the moments of pressure. We need to get the moment to jump in otherwise, otherwise the midfielders get overloaded.
"The result is very bad. ery bad on us. But I think there are two ways of looking at this game. The goals could have been avoided from our side. On the ball, we were very positive and very brave playing the ball forward."