The Brazilian played the full 90 minutes as City humbled David Moyes' side in the first Manchester derby of the season in September, and he has revealed he expected such an illustrious opponent to prove a tougher test in his first encounter with the club.
City travels to Old Trafford on Tuesday and Fernandinho is confident of a similarly one-sided game but admits the atmosphere of a derby makes any game unpredictable.
"It was the first time I’d played them after joining City," he told reporters. "United are a club with history, with very good players and they were the champions. So I was surprised at how badly they played, how easily we won. The situation is different now, because we’re fighting for the title and they’re not. They’re just fighting for honor now. But a derby is the same whichever country you are in – each team wants to win.
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"We’ll go there expecting to win, but we know in a derby a lot of things can happen. We’ll be ready for it and have to play well because it’s a very important game for us."
City comes into the game off the back of a 5-0 win over Fulham, where Fernandinho was joined on the score sheet by Yaya Toure, who netted a hat trick, and defender Martin Demichelis.
"The midfielders are doing well right now and I think it’s the right moment for us to be in good form," Fernandinho said. "It’s important because our strikers are not scoring at the moment.
"We hope our strikers can get back to the way they were at the start of the season. But until then, we’ll carry on trying to score the goals for them.
"But we can’t go thinking that their midfielders won’t score against us. We need to be careful."