Vietnam U23 vs South Korea U23 in the 2026 Asian Games quarter-final: the space behind the full-backs

At the training ground in Chiba, late afternoon on 24 September. Around fifteen U23 Vietnam players remain on the grass, and three of them are still standing after the coaching staff have already rolled up the cones. I have watched that footage many times — not to find a goal, but to find what appears when nobody is watching: the way a full-back turns his head toward his own goal before playing square, and the way the midfield line contracts by exactly seven metres the moment the ball is lost.

That detail is small. But in the men's football quarter-final at the 2026 Asian Games, kicking off at 17:30 on 25 September in Japan, U23 Vietnam meet defending champions U23 South Korea, and small details are all that is left.

At the 2026 AFC U23 Asian Cup in Saudi Arabia in January, U23 Vietnam beat U23 South Korea 7-6 on penalties after a 2-2 draw over 120 minutes, in the third-place play-off. Let me be blunt: that was a third-place play-off, not a knockout tie with everything on the line, and South Korea did not bring their strongest squad. That is why I do not use that result as the yardstick for this match.

At the 2026 Asian Games, the story is different. U23 Vietnam are missing Dinh Bac and several first-choice defenders. U23 South Korea have added nine players based in Europe and three overage players. They beat U23 Qatar 4-1 and U23 Saudi Arabia 2-0 to reach the quarter-finals as winners of Group D.

Captain Lee Gi Hyuk of Gangwon FC, one of the three overage players, told The Chosun he had reminded his team-mates not to switch off, because U23 Vietnam had just lost to U23 Uzbekistan and would enter the quarter-final with great determination. Lee Gi Hyuk can play both centre-back and defensive midfield; he bruised his shin in a collision in the 27th minute against U23 Saudi Arabia but finished the game.

Korean media have issued similar warnings. Sports Hankook wrote that although coach Kim Sang Sik will not be on the U23 Vietnam bench, U23 South Korea must not be complacent. The paper identified two Vietnamese weapons: pragmatic defensive organisation, aggressive pressing in midfield, and quick counter-attacks into the space on the flanks. It called their most frightening quality not the names of the players, but their durable physical base and a mentality with nothing to lose.

I agree with most of that, but it needs to be placed in the right spot.

The problem lies in the space behind the Korean full-backs — where the gap in squad quality no longer protects anyone.

Korea's European contingent brings what youth teams in Asia usually lack: decision-making speed under pressure. But it also brings a very specific weakness. Players based in Europe are used to their forward line pressing continuously, which means full-backs are permitted to push high and do not have to drop immediately when the ball is lost. At youth international level, that synchronisation is never complete after a few sessions. The space behind them will open every time Vietnam play long through the middle.

This is where I come to transitions.

"Everything in football is a transition, including for the people who are not good enough to understand it." I wrote that years ago, after a match in which a midfielder was praised for running 11.8 km. In that game he ran 11.8 km, and 4.2 km of it was running toward a ball that had left long before. Distance covered is the most deceptive metric still packaged as a measure of effort.

U23 Vietnam do not need to run more than U23 South Korea. They need to run correctly in the first three seconds after winning the ball.

The way U23 Vietnam lost to U23 Uzbekistan shows the problem clearly. The goal came from a situation where the midfield dropped into position but the forward line could not hold the ball long enough for the block to push up. When you clear without an anchor, the counter-attack becomes a long ball to the opponent. In the January win over South Korea, by contrast, Vietnam did not dominate the ball. They kept the block compact inside 25 metres for 120 minutes and forced Korea to pass sideways in front of the box — the exact pass I watched on the training pitch in Chiba.

Possession percentage is the most deceptive metric in football. A team can chew up 60% of the ball with meaningless sideways passes and still lose.

In the other direction, South Korea have reason to worry about Lee Gi Hyuk himself. A 27-year-old centre-back who doubles as a defensive midfielder is a solution for a game that needs control, not for a game that needs speed. If U23 Vietnam can drag the tempo down, Lee Gi Hyuk benefits. If U23 Vietnam keep switching play to the flanks and force Korean full-backs to track back vertically, the fitness of a player who has just bruised his shin becomes a variable.

And this is where I part company with the crowd.

The "nothing to lose" mentality Korean media fear is not a mental quality. It is a tactical state, and it only survives for about the first 60 minutes.

After the 60th minute, as fitness drops and the score stays level, the weaker side usually starts playing not to lose, and that is when they lose. I have watched enough AFC U23 matches to see the pattern repeat: the defensive block holds its structure through the first half, then loses it because one individual decides to push forward hunting a winner. If U23 Vietnam want to progress, what they need is not a heroic moment but a disciplined kind of boredom in the final thirty minutes.

There is one detail in the match information few have noticed: coach Kim Sang Sik will not be on the U23 Vietnam bench. In youth football, the absence of the person making decisions from the touchline affects more than substitutions. It affects whoever fixes the structure when the opponent changes shape at half-time. U23 South Korea, with nine European-based players, can change formation mid-match with almost no loss of rhythm. U23 Vietnam cannot.

That is the real margin of error in this game.

People laughed at me for betting on a child; five years later they ask me what I saw. I still work the same way. The 2026 Asian Games quarter-final will not be decided by who has more European-based players. It will be decided by whether U23 Vietnam can keep their block inside 25 metres for the final thirty minutes — and by whether someone on the bench has the nerve to change nothing at all when the score is still 0-0 in the 75th minute.