Saudi Arabia fell behind after 11 minutes on Wednesday, Ryang Yong-gi giving North Korea the lead in Melbourne, and initially struggled to break down Jo Tong-sop's stubborn side.
But the Gulf nation's superior quality eventually told, with Olaroiu's men going in level at the break thanks to Naif Hazazi before pulling away in the second half.
A double from Mohammad Al Sahlawi effectively settled the game. And the gloss on a fine recovery was applied when Nawaf Al Abid hit home on the rebound from his penalty - which struck both posts - after Lee Yon-jick had handled a shot from Salem Al Dawsari's that had initially hit the crossbar.
According to Olaroiu, waiting for his team's dogged opponents to wear themselves out was always part of the plan.
"I was confident because it's difficult to play the way North Korea play for the entire game," said the Romanian coach.
"We made them tired and knew they would concede spaces. We chose to play with two strikers, which is why we lost something in the middle.
"It was a problem there for a while. They scored and were very dangerous on the counter-attack but sometimes you have to take risks."
Next up for the Saudis is a game against Uzbekistan on Sunday, with a spot in the quarter-finals, and a clash against Australia or South Korea, the reward.
Asked if he was now hopeful of advancing from the group, Olaroiu offered a bullish response: "If we don't have confidence, what do we have?
"It's important to pass this moment very quickly, as we did the game against China, and to think about the next game, with a different team and a different way of playing. We have to concentrate."
With North Korea eliminated, Jo must now prepare his players to face China, although he insisted they will be doing their neighbours no favours.
He said: "Although we know the final result of this competition for our team, we have one final match and we will do our best to win this match in the spirit of fair play."
