The 25-year-old, who has not scored for his country in 16 months, crashed a long-range effort against the post with 11 minutes gone shortly after being cautioned.
Ronaldo was confronted by Ivorian defender Guy Demel after Uruguayan referee Jorge Larrionda had waved away his claims for a foul as he surged forward, and both men were cautioned.
The Portugal captain later said: "Sometimes it's difficult that the referee doesn't give fouls because he thinks I dived.
"I know the game is very quick and the players are very quick, but sometimes I don't understand the decisions of referees.
"I respect them, but sometimes I don't agree because they don't protect the dangerous players.
"In the first half, someone tackled me and I was given a yellow card. I didn't do anything, but he gave me a yellow card.
"Sometimes I don't understand, but that's football. I know I don't have to react if I get a yellow card. I don't want to speak about the referee. I respect the decision and I want to be focused on helping my team and to do my best."
In a game of few clear-cut chances, Ivory Coast gave as good as they got, but there was little doubt that the Africans and their manager, former England boss Sven Goran Eriksson, were the happier after a positive start to their World Cup adventure.
Asked to compare working with the two international teams, the Swede said: "The only difference now, I must say, is it's a smile all day.
"If we are travelling or we are doing whatever we are doing, it's an extremely happy football team. If the players have had any problems between them in the past, I can't understand it."