"It was the complete performance as far as we were concerned," said Powell. "It's the first time this season we have been able to say that.
"The midweek victory over Cardiff gave us confidence and today we defended solidly when we had to, as well as causing problems going forward.
"City were desperate for the points themselves so I am thrilled we competed so well. It is a result and a performance to build on."
Sunday's victory has lifted Charlton up to 16th place in the Championship table.