Koo denies Ghana a draw
The Wolfsburg midfielder scrambled home from close range after Asamoah Gyan - who also missed a first-half penalty - had cancelled out Ji Dong-Won's opener.
Just as in the 2-1 win over Serbia on Friday, the hosts took an early lead when Ji climbed above the Ghana defence to head a Ki Sung-Yong corner into the net. Ghana goalkeeper Richard Kingson got his hands to the ball but could not keep it out.
Just three minutes later, Hong Jeong-ho brought down Gyan in the area but the Sunderland striker saw his low penalty comfortably saved by Jung Sung-Ryeong. Both teams continued to have chances. Jung saved from Gyan soon after and Ji had a chance to add a second when through on goal but could not lift the ball over Kingson.
The game continued in the same vein after the break. Monaco striker Park Chu-Young hit the crossbar with a 25-yard rocket on the hour but after 64 minutes, Ghana were level. Sulley Muntari's pass split a static defence leaving Gyan to slot a low shot past the previously impressive Jung.
The game was heading for a draw when Ji headed across goal in injury time to leave Koo with a simple finish.