Ronaldo got on the scoresheet at last as the Portuguese put themselves in prime position to accompany Brazil into the second round after a scintillating display of attacking football.
Portugal coach Carlos Queiroz had said he would approach the game in three stages - win, score goals and then look at the standings - and his players followed the plan to the letter.
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"It was a great display, good goals, great attitude. We needed a moment like this, a well-played game so that the motivation and confidence can be even bigger now," said Queiroz.
"It's a big result, but it's another game and we still haven't won anything yet. Now we have to think of qualifying for the next round, one game at a time, try to win the next one with the same ambition with which we approached this game."
The Ivorians, beaten 3-1 by Brazil on Sunday, have one point and a draw for Portugal in their final game would in any case guarantee that Queiroz's side progress to the last 16.
North Korea's amazing journey, though, has suffered a terminal blow and coach Kim Jong-hun said he took responsibility for the heavy defeat for "not planning the right strategy.
"...our players, I think, played to their full potential," he said. "However, tactically speaking, I think it fell apart so we couldn't block their attacks and that's why they scored a lot of goals.
