In stoppage time, masked Tottenham star Son Heung-min raced across the pitch and played through to substitute Hwang Hee-chan, narrowly cleared for offside, whose free made it 2-1 to South Korea.
There was crazy joy among players and fans.
South Korea depended on the Uruguay-Ghana result to advance and when South Korea made it 2-1, a despondent Luis Suarez was visible in Uruguay.
There they had ten minutes left to play when South Korea finished their match.
Already through to the last eight, Portugal, who aired several players but Cristiano Ronaldo played, looked to extinguish South Korea's hopes when Ricardo Horta made it 1-0 in the fifth minute.
Pepe hit a ball deep and Diogo Daolot played it diagonally inwards to Horta who pounced directly.
However, South Korea regained hope when Kim Young-gwon equalized at 1-1 after just under half an hour.
Ronaldo had the ball on his back after a corner and Kim Young-gwon struck from close range.
Ronaldo had a couple of chances, including a free-kick which he burned in the first half.
In the 65th minute, Ronaldo was replaced.