Nigeria have booked their place in the knockout stages of the Under-20 World Cup with a 1-0 victory over South Korea in Istanbul.

The African nation made a strong start to the match, forcing several early set pieces before Olarenwaju Kayode headed home Abdul Ajagun's delivery with nine minutes on the clock.

They almost doubled their lead six minutes later when Onyinye Ndidi headed Ajagun's corner wide from close range.

Nigeria continued to be a threat and almost found a second goal when Abdulahi Shehu diverted Ikechukwu Okorie's downward header narrowly over the bar.

South Korea, who had offered little attacking threat in the first 45 minutes, began to test Nigeria in the second half, forcing goalkeeper Chukwunenye Okani into several saves.

However, neither side could find another goal as Nigeria secured second place in Group B, with South Korea finishing two points behind in third.