Behind the 2026 AFF Championship Triumph: Kim Sang-sik, Nguyen Xuan Son, and Vietnam's Balancing Act

Rajamangala Stadium tunnel, January 5, 2026, 7:40 PM. Nguyen Xuan Son tied his shoelaces one last time, put his left foot onto the bench, balanced himself on his right leg, then looked toward the corridor where the Thai players were advancing. He said nothing; the whole team said nothing. In football, the first strike is never the fastest, but it teaches us how to keep balance. The AFF Cup 2026 final second leg was never simply a match; it was a test of who could stay calm enough to stand firm when the wave of pressure rose from the stands. I first sat in the commentary booth at My Dinh Stadium in the early years of my career, and I remember clearly the feeling when Vietnam defeated Thailand to win the 2026 AFF Cup. Back then, coach Park Hang-seo was celebrated as a tactical master who elevated Vietnamese football. But the 2026 triumph carries a different color: it did not come from a celebrated coach, but from a quiet South Korean who was initially viewed as just a stopgap solution after Philippe Troussier's failure. The context of 2026 was full of skepticism. Kim Sang-sik took over Vietnam during a crisis of confidence. The team had failed at the 2026 World Cup qualifiers and had not produced any truly convincing display in friendlies. Experts wondered whether a former South Korean defender, used to organized and disciplined football, could read the pulse of Vietnamese football. Kim's openness showed in his methods: he did not copy Park Hang-seo's lesson plans, did not create a pale clone, but quietly reformed the team from within. If one simply looks at the 5-3 aggregate win over Thailand and concludes that Vietnam are far stronger, that would be a superficial reading, because Southeast Asian football has changed enormously since 2026. Thailand then possessed the generation of Chanathip Songkrasin and Theerathon Bunmathan playing fluid possession football. By 2026, Thailand still controlled possession, but they were far weaker against physical pressure in wide spaces. Vietnam under Kim Sang-sik exploited exactly that weakness using something many did not expect: tactical flexibility. Vietnam's tactical setup in the final was not a fixed number but continuously shifted. Without the ball, the team formed a 5-4-1 block with a back three of Do Duy Manh, Nguyen Thanh Chung, and Bui Tien Dung. When the team had the ball, the two wing-backs advanced to create a 3-4-3. The key point was not the numbers but how Kim assigned clear roles to each player. Nguyen Hoang Duc was consistently dragged back between the two central defenders for build-up play, while the Vietnamese Golden Ball winner could still push up like a box-to-box midfielder. This positional rotation left Thailand's midfield continually guessing which player would receive the ball from the defensive line. The biggest bright spot of Vietnam's campaign was finding a centre-forward capable of stretching the opposing back line. Mbappe once taught me a great lesson at the 2026 World Cup: Mbappe does not run across the pitch; he runs over the fear of the defense. Nguyen Xuan Son does not possess Mbappe's speed, but he has enough physicality, skill, and intelligent movement to prevent Thai centre-backs from stepping up. When the opponent's central defenders were forced to drop deep to mark Son, the space behind Thailand's midfield immediately opened for wingers like Nguyen Dinh Bac and Pham Tuan Hai. The opening goal in the second leg at Rajamangala was a perfect example of this dynamic. Xuan Son did not charge into the penalty box to receive crosses; he dropped into the central channel and pulled Thailand's centre-back out of position. The space behind the full-back was then exploited by a long diagonal pass from Nguyen Quang Hai. It was a seemingly simple movement, but it proved how well the collective understood each other's tactical intentions after months of drilling. Notably, Kim Sang-sik did not build the game solely around one naturalized centre-forward. He created a deep defensive system that prevented opponents from building play comfortably. Instead of pressing across the whole pitch the way Troussier once did, Vietnam deliberately retreated into their own half, closed the central corridor, and only pressed when the ball went wide. This patience allowed Thailand to hold the ball a lot, but most of their passes were lateral or backward. Looking at possession stats, one might think Thailand dominated, but possession is the most deceptive metric in modern football: some teams farm sixty percent of the ball with harmless sideways passes, and the 2026 final is a classic example. I rewatched the first leg at Viet Tri on January 2, 2026, several times, and the most striking detail was not the goal-scoring moments but the rhythm of Vietnam's team when they lost the ball. Losing possession on the right side, the whole team immediately compacted into a 5-4-1 block in their own half. Losing it in midfield, only the two wide forwards immediately pressed while the midfield four dropped into a tight circle. This discipline did not come from some distant tactical manual but from a deep understanding of each individual's role. Kim Sang-sik worked quietly with every player on one-touch and two-touch passing patterns, which helped them stay physically balanced throughout the ninety minutes and across both legs. One differentiating factor of this victory compared to previous titles was the ability to shift mental states at different moments of the match. In the second leg, Thailand surged after their equalizer, and the Rajamangala crowd seemed ready to swallow the Vietnamese players. But precisely in those moments when the stands screamed the loudest, the away side showed astonishing composure: they did not panic-clear the ball, were not afraid to slow the tempo, and understood that the more Thailand pushed forward, the more space would open up behind their defense. One cannot ignore the image of Nguyen Xuan Son suffering a serious injury in the second leg. When a player who had been scoring and assisting constantly had to leave the pitch on a stretcher, his team usually falls into chaos. Vietnam under Kim Sang-sik proved the opposite. Son's departure removed the team's attacking focal point, but it simultaneously made the remaining players simpler and more efficient. They no longer searched for spectacular passes; they played direct attacks into the space Thailand left open in the final minutes. However, if we simply celebrate the championship unconditionally, we will miss several dangerous blind spots. Vietnam's 2026 success carried significant dependency on Xuan Son. Without him on the pitch, the attack has no true centre-forward capable of holding up the ball under physical duress. Replacements such as Nguyen Van Toan or Nguyen Tien Linh have limitations in physical presence and ball retention under pressure. Xuan Son's broken leg during the tournament makes the road to bigger goals such as the 2027 Asian Cup or the 2030 World Cup qualifiers highly uncertain. The second problem lies in the squad depth of the next generation. The golden generation of Vietnamese football, including Quang Hai, Hoang Duc, Duy Manh, Tien Dung, and Van Thanh, have all passed the age of 27. They are in their most mature period, but equally in a phase where physical durability can easily decline without careful management. Looking at Vietnam's bench in the final, there was rarely a young substitute who provided real reassurance in the way Dinh Bac did at the 2026 AFF Cup. Kim Sang-sik can build his own playbook, but he will have to face a greater question: how can Vietnamese football not only win a regional tournament but also survive against football cultures of a higher level? There is a comparison I always use in my commentary work: football pitches and esports are similar in that the winner is the one who reads the breathing rhythm of the majority. At the 2026 tournament, Vietnam read their own breathing rhythm. They were no longer the wildly energetic team that charged forward while forgetting to come back. They became a well-drilled collective, knowing how to stay silent at the right moment, and how to accelerate at the right moment. When the stands fall silent, only then do we clearly hear our own applause. In a match as chaotic as the second leg final at Rajamangala, Vietnam heard their own inner applause very clearly. That was not the noise of a nation going ecstatic over the word championship; it was the stability of a team that learned how to keep balance through years of ups and downs. The open question is whether Coach Kim can go further, and whether Vietnamese football dares to aim at something bigger than another regional trophy. I believe this generation still has a chance to achieve something greater than a Southeast Asian title. They now possess a fighting spirit forged through countless difficulties. They have a clear operating system. They are waiting for a sufficiently big stage, and as long as they maintain the balance between passion and rationality, the story of Vietnamese football's journey toward Asia will not end.