The Flying Eagles, who eliminated hosts and six-time champions Argentina in the Round of 16 on Wednesday, created few chances in spite of passing the ball round the field quite well.
They were clearly lacking the necessary punch in the final third.
Victor Eletu, whose show of guts and grits led to the second goal that ended Argentina’s hope on Wednesday, curled a fine shot from outside the penalty box on the half hour.
But the Korean goalkeeper punched it out of danger.
In a highly cagey affair, both teams watched each other closely and only few risks were taken throughout the first period.
In the second period, Nigeria looked more adventurous with defender Daniel Bameyi striking from the edge of the penalty box, only to see his effort stopped by the goalkeeper.
In added time, Emmanuel Umeh’s dazzling run ended with a shot that was also smartly held by the Korean goalkeeper.
The Asian vice-champions got the winner five minutes into the first period of extra time, when substitute Sun Choi met a corner-kick with a glancing header.
Umeh, with a great chance to equalise in the 109th minute, blazed over the bar, and in the final minute, struck the side of the net.
The News Agency of Nigeria (NAN) reports that the Flying Eagles will now return to Nigeria on Tuesday.
South Korea will face Italy in the semi-finals on Thursday.
