Since being hammered 6-1 by City at Old Trafford last month, United have won five successive matches in all competitions without conceding a goal.
Defensive frailties had been hampering the Red Devils during the early weeks of the season and Ferguson feels injuries have unsettled the balance of his team.
However, ahead of Tuesday night's Champions League tie with Benfica, Ferguson is pleased with how United have built momentum since the City humbling.
"The players have addressed the situation well and the collective response has been good," said Ferguson.
"At this stage of the season what we try to do is get through to the New Year near to the top. Top would be fine, but to be near the top would mean the run-in would present us with an opportunity.
"We have won five games in a row. That is momentum. We have had a few issues which, hopefully, we are gradually getting over.
"We have all worked really hard defending and, when you get the ball, you hope you produce enough football to win the match.
"Injuries always play a part. It does unsettle the balance of the team at times and sometimes we do have to rethink.
"We have Anderson and Tom Cleverley injured. Michael Carrick played his first game for a while on Saturday. Darren Fletcher has been out. We have made some changes to the team from the start of the season, which you don't envisage when you see them all fresh.
"We went through the United States pre-season tour without a single injury and then you get hit with a list of them."