The SEA Games champions beat Malaysia 2-0 in the Group C match on June 8 in Tashkent, Uzbekistan, to qualify for the last-eight round for the second time, where they will play the winner of Group D, either Japan or Saudi Arabia.
The previous time, Vietnam lost to Uzbekistan 1-0 in the last seconds of extra time in the final in 2018.
Thailand and Malaysia are the two ASEAN teams that have qualified once.
At the post-match briefing, head coach Gong Oh-kyun said: "Vietnam pocketed its first win at this tournament and earned a berth in the quarters, although no one thought we could make it before the competition."
"I am impressed with my players. I have done nothing, and it was all their hard labour."
Asked why he placed new faces in the midfield in the final group match, the Korean coach explained: "There is no special reason. I have thought about the quarter-finals already, so I made my plans for this match. My players all have good fitness and are professional, so I bravely made changes."
Gong said he did not care much about the next team because they were all difficult. His team would focus on recovering first and discussing tactics later.
"We have not celebrated yet, because there are matches ahead. I asked my players about what they wanted. The answer was a new higher level. I understand and will bring them to a 'new land,'" Gong said.
On the Malaysian side, coach Brad Maloney was disappointed with his team's third loss in a row and being knocked out.
He said his players began the match well and played positively. But the penalty and the red card made it difficult to change the game.
After two draws and one win, Vietnam are in second place in Group C, below the Republic of Korea who have two wins and a draw.
The Vietnam Football Federation will give a 600 million VND (26,000 USD) bonus for the team.
Prime Minister Pham Minh Chinh and Minister of Culture, Sports and Tourism Nguyen Van Hung send their congratulations to the young players.
PM Chinh encouraged the U23s and asked them to well prepare for the next match. He wants the players to compete with a spirit of fair play and for the nation's pride./.
