Ahmed Ali Alabry scored in the final seconds of extra time to give the United Arab Emirates a 1-0 win over the South Koreans in the second semifinal Tuesday.
Nagai, the tournament's leading scorer with five goals, had been in doubt for Tuesday's game after limping off the field in Japan's quarterfinal win over Thailand.
“The injury didn't bother me at all. All I was thinking about was to win the match,” he said.
Iran's Arash Afshin opened the scoring in the 6th minute, the first goal Japan had conceded in the tournament.
Japan's Kota Mizunuma equalized in the 38th minute.
Japan has been favored to win the men's football title, but faced a difficult challenge from the physical Iranians, who took six shots on goal to Japan's four.
The South Koreans had 11 shots on goal, including a powerful header from Hong Jeong-ho that went directly into the arms of goalkeeper Khaseif Housani, but were unable to convert the chances into a goal.
The UAE scored after South Korea had pulled starting goalkeeper Kim Seung-gyu in anticipation of a shootout. The Korean defense was out of position as the UAE launched its final attack, with Alabry driving a shot past replacement keeper Lee Bum-young.
