A goal will perhaps have been especially sweet for Ronaldo, who had walked out of a news conference on Tuesday after being questioned about his record in away matches this season.
He had not netted away from the Bernabeu since 29 November and, although he was quiet for large periods of Wednesday's game, a clever bit of skill produced the breakthrough.
Chasing on to a long pass, Ronaldo took one touch to bring the ball under control and gave himself a sight of goal before firing into the top corner, with his effort taking a nick off Roma skipper Alessandro Florenzi.
The 31-year-old could have had more after that, notably heading just wide of the far post, but the strike means he now has five away goals in the Champions League this season; more than any other player.