The Blues were expected to defend deeply at the Etihad Stadium, but an attacking display saw them come away with a 1-0 victory.
Branislav Ivanovic scored the only goal of the game as City were beaten at home in the league for the first time this season.
"This is where [Mourinho] comes into his own," Terry told the club's official website. "We spent a good couple of days working on their strengths and weaknesses.
"They were long sessions for us but they were very worthwhile. It was a really important win. Man City have been phenomenal at home, scoring goals and rolling teams over.
"For us to come here and not only get three points for ourselves but to show other teams they can be beaten is an eye-opener for everyone."
Monday's win has seen Chelsea move level on points with second-placed City in the table.