South Korea captain Jang Hyun-Soo converted a penalty two minutes from time Sunday to beat arch-rivals Japan and secure a place in the Asian Games semi-finals.

Victory over Thailand in the next game could see the South thrown into a final with another rival, North Korea, who must thank Jong In-Gwan for an injury-time goal as they beat United Arab Emirates and reached the last four.

Thailand beat Jordan 2-0 while North Korea face a tough tie against Iraq, who downed Saudi Arabia 3-0 with veteran striker Younis Mahmoud returning to haunt the Saudis.

Mahmoud, who hit the winner in Iraq's 2007 Asian Cup final win over the Saudis, got two goals this time to inflict more misery on the country where he plays his league football.

South Korea missed countless chances to break the resistance of a young Japanese side in front of 43,000 raucous fans, many wearing flashing "Red Devils" horns.

Jang calmly tucked away a spot kick in the 88th minute after substitute Lee Jong-Ho had been clattered from behind by Ryota Oshima and left with blood pouring from his nose.

South Korea's players will be excused two years of mandatory military service if they win the tournament, which is played under the Olympic under-23 format.

South Korea will have to improve their finishing, however.

Kim Young-Uk missed a point-blank header and Lee Yong-Jae had a shot cleared off the line in the first half. Lee Jong-Ho also had an effort blocked on the line as South Korea piled on the pressure after the break.

North Korea's Jong scored in the third minute of injury time in another of the quarter-finals in which both sides were guilty of missing chances.

With just seconds left, Jong, who scored twice in the second-round win over Indonesia, got a shot on target from the edge of the penalty area that sent their hardcore fans in the ground into raptures.

Thailand will play South Korea after beating Jordan 2-0 through goals from Chanathip Songkrasin and Thawikan Kroekrit.

Thailand's Chanathip, known to his fans as 'Messi J', hit an easy shot from the edge of the penalty area in the 37th minute.

Thawikan fired home in the 70th minute after the Jordanian defence had desperately kept two earlier attempts out of the net.

North Korea face the toughest semi-final, with Iraq finding goal-scoring no problem at this Asian Games contest. They beat Indonesia 4-2 to reach Sunday's game.

The 31-year-old Mahmoud, one of the allowed over-age players in the Iraqi side, scored twice in the opening half-hour. His first was an easy header and for the second he put away a low cross into a near-empty goal.

Saif Almohammedawi pushed the third goal into the net off his body in the second half.

The two Asian Games semi-finals are on Tuesday and the final next Friday.