There were few clear chances for either side during the first half which ended in a 0-0 draw.
However, in the 75th minute, Japan’s Omotehara Genta, who just came onto the pitch during the match, put the pass from Ochi Yamato into the right corner to give his side a 1-0 lead.
Vietnam later attacked in a failed effort to level the score when they faced strong defense from Japanese players.
Vietnam and Japan both earned early tickets to the semifinals after defeating Australia 1-0 and 4-3, respectively though Vietnam lost 3-2 to Japan in the last match of group B in the qualifying round on Tuesday.
In the semifinal round, Vietnam crushed Myanmar 4-1 while Japan defeated their Thai rivals 2-1.
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