Cristiano Ronaldo ended his 16-month international goal drought but the damage had been done long before his late strike as the 2006 semi-finalists put themselves in prime position to accompany Brazil into the knockout phase.
Portugal's scintillating display of fast-paced attacking football also ended North Korea's hopes of progress.
Raul Meireles had put them 1-0 up by halftime and three goals by Simao Sabrosa, Hugo Almeida and Tiago in a seven-minute blitz early in the second half, broke the Korean resistance.
Another clutch of three goals by substitute Liedson, Ronaldo and Tiago in the last 10 minutes had the substantial Portuguese following in seventh heaven.
It also emphatically ended the "Cape Town Curse" that had seen the city's three previous games produce dull draws and just two goals.
"It was a great display, good goals, great attitude," said Portugal coach Carlos Queiroz.
"It was a great day for Portugal and Portuguese football and now we will concentrate on the next game. Although we got seven goals we only got three points."
Despite his caution, Portugal's plus-seven goal difference makes the win effectively worth a bonus point.
They have four points to the six of Brazil and on the evidence of Monday's display will go into Friday's Durban clash full of belief that they can beat the five-times champions.
Ivory Coast, beaten 3-1 by Brazil on Sunday, have one point and need a Portuguese defeat combined with a massive win for themselves over Korea to have any hope. A draw for Portugal in their final game would guarantee Queiroz's side progress.
EMPHATIC RESULT
Monday's emphatic result looked unlikely as North Korea started with unexpected ambition and had one or two near misses.
Ricardo Carvalho thumped an early header against a post but in conditions made difficult by relentless rain it took until the 29th minute for Portugal to find a way through.
Tiago, drafted in for the injured Deco, rolled a beautifully weighted ball to Meireles who fired home low and hard.
Portugal gradually took command after that and changed the dynamics of the match, and group, with three well-made goals.
Meireles and Almeida combined well to set up Simao to tuck in the first of them after 53 minutes, Fabio Coentrao crossed for Almeida to head home the next after 56 and Ronaldo put another goal on a plate for Tiago on the hour.
As space began to open up, Portugal took full advantage with some devastating moves. Ronaldo hit the bar in the 70th before Liedson came off the bench to smash in the fifth after 81.
Ronaldo eventually got on the scoresheet when Liedson robbed a tiring defender. Goalkeeper Ri Myong-guk challenged Ronaldo but the ball spun into the air and landed on the forward's head before he calmly volleyed it into an empty net.
Tiago, another one of Queiroz's inspired changes to his starting
