Vietnam U23 Meet South Korea U23 in the 2026 Asian Games Quarter-Final: When a Depleted Defence Turns the Flanks into a Double-Edged Sword

The 88th minute of the third-place play-off at the 2026 AFC U23 Asian Cup in Saudi Arabia, the ball sits on the penalty spot. I was watching with a notebook in hand as the shoot-out ended 7-6 in favour of Vietnam U23, after a 2-2 draw across 120 minutes. South Korea U23 left the pitch that day with the look of a team that had just lost something. Less than nine months later the two sides meet again, this time in the quarter-final of the 2026 Asian Games at 17:30 on 25 September in Japan. The context has flipped entirely. Vietnam U23 now walk into the match in a very different posture, forced to live off what remains rather than from the position of the side delivering the decisive blow as they did in January.

From the stands at Luzhniki I learned that a formation is only paper while the match lives in the people. That is exactly the puzzle in Japan this time: two completely different sheets of paper, but it is the people on the pitch who decide.

Who has gained and who has lost before kick-off

At the U23 Asian Cup in January in Saudi Arabia, South Korea U23 lost to Vietnam U23 on penalties. It was a shock for Korean football, but the reality deserves a closer look. Vietnam U23 had a full squad then, with Dinh Bac in the line-up, and a defence deep enough to absorb pressure across the full 120 minutes.

At the 2026 Asian Games the picture has reversed. Vietnam U23 are missing Dinh Bac along with several key defensive players. South Korea U23 have added nine new players based in Europe plus three overage players. This is a rebuild of the spine rather than a change of shirt.

With that squad, South Korea U23 beat Qatar U23 4-1 and Saudi Arabia U23 2-0, reaching the quarter-finals as winners of Group D. They won by controlling matches from start to finish, without needing stoppage-time goals to settle their fate.

The notable detail lies elsewhere. In both group matches, South Korea U23 allowed their opponents chances across the opening 20 minutes of the first half. That is the window in which they are still assembling the team, still finding the rhythm between the Europe-based group and the domestic group. For a side stitched together from many sources, that stretch is the most sensitive zone.

On Vietnam's side, the loss of several defensive pillars forces changes to the centre-back pairing and the full-back positions. In modern football, the back line is where understanding must be accumulated over many matches, and it cannot be assembled overnight. When two centre-backs do not yet read each other, the gap between them opens, and every good striker knows to run into it.

Head coach Kim Sang Sik was not on the bench for Vietnam U23 in this match. The detail is rarely mentioned but directly affects the ability to pivot the game plan mid-match. A team without its head coach on the touchline is slower to read the tempo and adjust the shape when the game turns.

The Korean captain and an unusual level of caution

Captain Lee Gi Hyuk of South Korea U23, currently at Gangwon FC and one of the three overage players, warned his team-mates not to be complacent against Vietnam U23 in the quarter-final.

Speaking to The Chosun, Lee Gi Hyuk said: "Vietnam U23 have just suffered a defeat to Uzbekistan U23. So they will come into the quarter-final with huge determination. I have therefore reminded my team-mates that we cannot afford to switch off and must maintain full concentration."

Lee Gi Hyuk can play as a centre-back or a defensive midfielder. He picked up bruising to his shin after a collision in the 27th minute against Saudi Arabia U23 but completed the match, and is fully available to face Vietnam U23.

Korean media also believe head coach Lee Min Sung's side must be careful against Vietnam U23. Sports Hankook warned: "Even though head coach Kim Sang Sik is not on the Vietnam U23 bench, South Korea U23 absolutely must not be complacent."

The outlet judged that Vietnam U23 still possess traits that can trouble South Korea U23, especially their ability to organise defensively and switch quickly into attack.

Sports Hankook commented: "Pragmatic defending, aggressive pressing in midfield and quick counter-attacks into the spaces on the flanks are Vietnam U23's weapons. Their most frightening quality lies in their durable physical foundation and a mentality with nothing to lose."

The flanks: weapon or trap?

That final line from Sports Hankook deserves a careful read. The flank spaces are where Vietnam U23 counter, but they are also where they are most easily punished when they lose the ball.

Inside a deep defensive block, Vietnam's two full-backs must choose between pushing high to create width for the counter, or staying back to hold the defensive line. When Dinh Bac was still in the forward line, he held the ball long enough for the full-backs to advance. Without Dinh Bac, the counter is shorter, the ball is held for less time, and the full-back pushes up only to turn back with lost momentum.

Against a side with nine Europe-based players in the squad, South Korea U23 have the quality to switch play from one flank to the other in two passes. They do not need to break the block with an individual dribble, only to move the ball faster than the block can rotate.

This is the crux: Vietnam U23 defend best when they are not forced to counter with both flanks at once.

How South Korea U23 build their attacks

A side with nine Europe-based players plus three overage players does not play hopeful long balls. They build along the vertical axis, starting from the centre-back pairing, through the defensive midfielder, then fanning out to the flanks.

The advantage of this approach lies in tempo control. The disadvantage lies in the number of passes needed to reach the opponent's box. To break through a deep block, a side building from the back needs at least 12 to 15 passes per attacking move. Every pass is a chance for the defending side to read the intention.

This is why Vietnam U23 need to press in midfield rather than high up. If Vietnam's forward pushes up alone, he burns energy without creating real pressure. If the midfield line holds its spacing and closes the vertical passing lanes, South Korea U23 are forced to push the ball wide, and the attack shifts from the centre to the flank, slowing by at least one beat.

One beat of delay in modern football equals 1.5 to 2 metres of space that the defensive line can recover. With a depleted back line, every metre recovered is precious.

Three overage players and the rhythm problem

The presence of three overage players brings an advantage that is rarely discussed: the ability to control the tempo of a match.

Young players tend to play on emotion, speeding up when excited and fading when behind. Overage players, especially those competing in professional domestic leagues, can hold a steady rhythm. Lee Gi Hyuk belongs to that group. He plays as a centre-back or defensive midfielder, meaning he can read the game from deep and adjust the defensive line's spacing situation by situation.

In matches where Vietnam U23 want to stretch time and find chances in the second half, the presence of a tempo-setter deep in the opposition ranks significantly reduces that possibility. South Korea U23 will not push themselves into a chaotic game over a single misplaced pass.

Physical foundation: the one intact weapon

One thing at Vietnam U23 is unaffected by Dinh Bac's absence or the missing defensive pillars: the physical foundation and the ability to press.

In modern football, pressing is not just running a lot. Pressing is running at the right time, in the right direction, at the right player. A good pressing side can make the opponent release each pass half a second slower, and half a second in a counter-attack is enough for a defender to recover.

Vietnam U23 have shown this ability in recent matches. The difficulty in the 2026 Asian Games quarter-final lies in the fact that South Korea U23 do not build with long balls over the top that fall into the pressing trap. They build with short, multi-beat passes along the vertical axis. To disrupt that, the pressing side must hold the spacing between lines for the full 90 minutes. That is the most demanding requirement in football, and it only becomes reality when a team has enough players who have played alongside each other long enough.

The blind spot: when "nothing to lose" becomes reverse pressure

Both captain Lee Gi Hyuk and Sports Hankook referenced Vietnam U23's nothing-to-lose mentality. It is a reasonable reading of the match, but it contains a blind spot.

A nothing-to-lose mentality works when the team still holds its defensive structure. Once a goal is conceded early, the team falls into a state where it must push up, and that mentality turns into having nothing left to lean on. The block breaks apart, the flank spaces open wide, and the match ends early.

Conversely, if Vietnam U23 keep a clean sheet through the first 30 minutes, the pressure shifts to South Korea U23. A side assembled from many sources will start questioning each other when they cannot score. Individual moments appear, the attacking structure loosens, and counter-attacking chances open up.

The blind spot in the Korean media lies in rating Vietnam's spirit highly while forgetting that spirit is a variable dependent on the scoreline. No team keeps that spirit when trailing by two goals.

Three frames to watch

My experience of watching matches tells me that every big game is usually decided by three spatial moments. For this quarter-final, those three frames are as follows.

The first is the 15th minute. If South Korea U23 have not scored and Vietnam U23 still hold the spacing between their three lines under 25 metres, the match tilts toward Vietnam U23 more than the initial forecasts suggested.

The second is South Korea's first set piece in the 25-metre zone. With a tall, Europe-based group, set pieces are the shortest route to breaking a deep block. Every set piece is a riddle, and I am only the reader of the pieces on the pitch.

The third is Vietnam U23's first counter-attack involving at least three players. If that move creates a chance, the whole team's belief rises significantly. If it fails for lack of numbers up front, Vietnam U23 will be forced into pure defending for the rest of the match.

Closing

When I stumbled in 2026, I understood that the audience does not need me to be right, they need me to be convincing. This 2026 Asian Games quarter-final will not be decided by the squad list on paper. It will be decided by how long Vietnam U23 can hold their defensive structure, and how much time South Korea U23 need to find a way to rotate that block. If Vietnam U23 get through the first 30 minutes without conceding, the match becomes an entirely different story from what the odds suggest. If the goal comes early, the flank spaces will tell the story the Korean media already warned about. For Vietnam U23 in Japan this time, keeping a clean sheet in the first half hour matters more than any attacking calculation.