The United captain spoke candidly about the transformation at Old Trafford in an interview with the Men in Blazers podcast, explaining precisely what changed when Carrick took the interim reins.
"Obviously we change some things. He changed some players, some players in positions. He tried different formations."
"And at the end of the day, we start scoring goals. We know we were creating a lot. In terms of creation and chances of goals, we weren't top when Ruben was here but we weren't finishing that — and then we were probably one of the best teams at not allowing teams in our box."
He identified a defensive frailty that had been costing the side.
"But when we allowed teams into our box, we would concede more goals. We start to be more compact when we defend. We understand we have moments where we have to suffer because we were not in an excellent moment, let's say."
Fernandes pointed to the first two games under Carrick — against Manchester City and then Arsenal at the Emirates — as a turning point in the mentality.
"I think that sacrifice we made in the first few games. I won't say lucky — but it was good for us that we had two big games straight away."
He explained why that pressure actually helped.
"Because if you win against City and then you don't have to face Arsenal who was top of the league and very difficult to play at the Emirates, you could think 'oh my god, it's going to be fine, we're playing great football now, we're going to win.'"
"I think City was the game we played the best. Against Arsenal, we didn't make the best game but we made the best of it. We found a way to win the game. Sometimes big clubs have to find a way of winning games, whether it's brilliant or not, you have to find a way of getting results."
United have won seven of ten games under Carrick and sit third in the Premier League. Fernandes has contributed three goals and nine assists in that run.
On his own future in Manchester, with one year remaining on his current deal, he was equally warm.
"Obviously when you're so long in a place, you kind of feel part of it. I'm very proud of my nation, I love my country. I love to be there."
"But I feel at home in Manchester. My kids feel at home here. It's wonderful for me to be in a place where my kids can enjoy so much and feel so much at home as they do in Manchester."
He ended with a smile.
"I felt Mancunian until I heard my kids speaking in English and having the accent and then I understand that I'm not as much as they are."