The Red Devils came up against a battling Royals side, with Wayne Rooney grabbing the eventual winner in the 21st minute at Old Trafford.
But although the United boss admits their rivals’ loss took some of the “edge” off Saturday’s game, the Scot warned his side that there is still a long way to go.
“Maybe it [the City result] took a bit of the edge off the game,” Ferguson said.
“You don’t get points and medals for being complacent and we won’t be. I think the players are conscious of the importance of the games now and that concentration, which has improved, has helped us do that [in terms of keeping clean sheets].
“It wasn’t a great performance but where we are today is not down to today but the last six months. The team has shown great consistency and played a lot of great football.
“Our goal difference is big over City now – 13 goals. It’s a great position to be in but the only thing we can do is win our next game.”
Ferguson, whose side host City at Old Trafford on 8 April, added: “We expected a tough game. They’re down at the bottom of the league and it happens quite often when a team changes their manager, they get a reaction.
“It was what expected. They’re fighting for their life at the bottom of the league and they came here very determined.”