The national U23 team advanced to the second round at the 2010 Asian Games despite a 0-1 loss to Iran in their final group stage match on Saturday.
Vietnam finished third in Group B behind Iran and Turkmenistan after a 3-1 win over Bahrain, a 2-6 loss to Turkmenistan and the Saturday defeat to Iran.
According to the rules, the top two teams from the six groups along with four best third-placed teams will advance to the next round.
Among the third-placed teams, Maldives with two points and Palestine with one point are behind Vietnam who has three points.
The Vietnamese players tried hard to force a draw with Iran, while the latter did not want to lose because it would put them in a difficult situation if Turkmenistan won.
The Iranians therefore were very defensive from the very beginning, making it difficult for their opponents to launch attacks.
Vietnam was in trouble after two minutes when goalkeeper Tan Truong took a goal kick standing outside the penalty area and Iran was offered a free kick.
Truong stopped a powerful shot but then he made a costly mistake, badly positioning himself while an Iranian player threw the ball from the right flank.
The ball found an unmarked Hosseini Seyed who headed it to the back of the net.
The Vietnamese had to try even harder to avoid a defeat, but were unable to create clear chances to score and equalize.
In the other Group B match, Turkmenistan drew 1-1 with Bahrain to be placed second in the group.
In the next round, Vietnam will clash with the Democratic People's Republic of Korea for a berth in the quarterfinals.
The match is likely to be a very tough one for Vietnam, with the Koreans finishing on top of Group C winning all three matches.