Ronaldo had missed four games due to a left leg injury before Madrid's 1-0 first-leg victory in the semifinals, where he helped to set up Karim Benzema's winner.
The Portugal forward, who was replaced by Gareth Bale in the 73rd-minute, said he ''was worried with it being my first game in three weeks.''
But he added: ''I felt great and I'll be ready for the next games.''
Ronaldo was involved in the majority of Madrid's goalscoring chances, forcing Bayern goalkeeper Manuel Neuer into a number of vital saves. But he also showed the effects of his injury layoff - missing one clear chance in the first half and declining to take a free kick that would normally have been well-suited for one of his thunderous, swerving shots.
''I didn't force anything to play, I felt good, so I played,'' Ronaldo said. ''Cristiano's back to help the team win.''
Ronaldo said some of the Madrid staff did not want him to play, but would not elaborate.
Coach Carlo Ancelotti said a decision was taken before the opener of the two-legged series.
''We have a nice advantage and if we score, we can complicate things for them,'' said Ronaldo, who has led Madrid to three straight Champions League semifinals but has yet to reach the final with the nine-time champions.
Ancelotti applauded Ronaldo's performance, especially since he played in a more defensive position as Madrid dealt with Bayern's control of possession. Ronaldo remains tied on a Champions League record 14 goals scored this season and will get a chance to set a new record in Tuesday's second leg in Munich.
''We took the decision for him to come out before the end, before the game. We didn't want to risk aggravating the injury,'' Ancelotti said. ''Ronaldo played well. He worked hard on the field to help defensively. He wasn't 100 percent but he sacrificed a lot tonight and on Tuesday he and Bale will be 100 percent.''
Bale nearly missed out because of sickness in his first appearance since his stunning winner in the 2-1 Copa del Rey final win over Barcelona one week ago.
Despite not being fully fit, Bale proved a perfect replacement for Ronaldo as he provided Madrid with pace and chances as Bayern pressed for an equalizer.