Ronaldo could have become the first player in history to score in four different European Championships after Zlatan Ibrahimovic had failed to find the net in Sweden's opening draw with Ireland earlier in the competition.
But it was Nani who instead netted for Portugal, only for minnows Iceland to fight back bravely and earn a draw thanks to Birkir Bjarnason's second-half strike.
It was a memorable night for Iceland, who are not only appearing in their first major tournament but also have a population of just 330,000 and are the smallest nation to play at a European Championship finals.
But Portugal skipper Ronaldo was less than impressed with what he saw during the game and after the final whistle.
"I thought they'd won the Euros the way they celebrated at the end," the Real Madrid star said, after seeing Portugal have 72 per cent possession and 26 shots on goal compared to Iceland's four.
"It was unbelievable. We tried hard to win the game and Iceland didn't try anything. This, in my opinion, shows a small mentality and they are not going to do anything in the competition.
"Portugal try to play football and try to win the game. Iceland didn't try anything. They were just defend, defend, defend and playing on the counter-attack."