The Spanish champions needed late goals from Karim Benzema and Ronaldo to turn a 2-1 deficit into a win in their opening Group D encounter.
"It was a very good game, for those who were watching," Ronaldo told TVE1 afterwards.
"We played very well. During the first half we created but missed opportunities, and in the second both Manchester City and us played well.
"We believed we could win and we did. The team has done very well, we knew we could do this and we did so on merit."
The Portuguese was asked about his celebrating of the winning goal, after he recently declared himself "sad".
"I celebrate when I have to celebrate. The match was very important and we are in the fight," he said.