The country’s under-23 football team went up against the Koreans on Wednesday at Pakhtakor Stadium in Tashkent, Uzbekistan.
Both teams had earned four points after their first two matches, while Vietnam played against Malaysia with two points.
South Korea scored the solitary yet decisive goal in the 35th minute after Go Jae-hyeon ran past the defenders and overcame the Thai goalkeeper in a one-on-one duel.
Both teams tried to score more goals but the match ended with a South Korean triumph.
Meanwhile, Vietnam beat Malaysia 2-0.
South Korea is now the leader in Group C with seven points while Vietnam heads into the next round with five points.
Thailand failed to qualify, earning only four points in three matches.