The Dutch had already made the last four, where they are likely to meet either Great Britain or Spain, but Republic of Korea had to win this clash to force Germany to get a result in the late game.
But they were 2-0 down at half-time after Mink van der Weerden scored his sixth goal of the tournament from a penalty corner and Valentin Verga added the second.
Only after Roderick Weusthof had converted a penalty stroke after he had been fouled in the circle did Korea start to play.
Nam Hyun Woo converted a penalty corner midway through the half, although he injured his back in the process and had to be carried off, while Jang Jong Hyun's set-piece was turned in by Lee Nam Yong.
I have no preference who we meet in the semi-finals. We feel very strong.Paul van Ass
But just as the Asian side looked like forcing some pressure, goalkeeper Lee Myung Ho was caught out of position wide on the left of his D as he went to close down the ball and was helpless to prevent Billy Bakker turning in the subsequent cross.
Netherlands coach Paul van Ass admitted that with nothing to play for the match had lacked some intensity.
'There was no pressure so it was difficult to play to a rhythm but I am glad we won the match,' he said.
'I have no preference who we meet in the semi-finals. We feel very strong.'