Ronaldo scored one goal and set up another as Portugal beat the Czech Republic to all but guarantee their progress to the quarter-finals.
But their lead was cancelled out nine minutes later when the impressive Libor Sionko headed in from a corner.
Ronaldo restored the lead on 63 minutes with a low drive before he set up Ricardo Quaresma for a tap-in late on.
It continued the trend so far in the tournament of every game being won by the team that scored first.
And it was a deserved victory for a Portugal team that improved after the interval and overcame a Czech side that responded to their coach's demand for them to improve after their unconvincing win over Switzerland.
"Our main aim was to get to the next phase. I'm very happy to have helped my team-mates to win," said Ronaldo.
"We played well in the first match and again in this match. If we carry on like this, we have a good chance."
Ronaldo added: "We played very well, although Czech Republic played very well in the first half. It was very difficult to penetrate their defence.
"We know how to sacrifice everything for the good of the team.
"We have now got a big chance but must respect our opponents because they too have a mission - they want to win, as we do."
Coach Luiz Felipe Scolari was surprised with the decision of opposite number Karel Bruckner to start with Milan Baros up front rather than Jan Koller.
"We had planned to play against a starting XI that would include Koller," he said.
"The fact Baros was there didn't make life easy. We faced difficulties because they had four or five in midfield and we had two wingers so we didn't know what to do."