Despite Portugal's lacklustre performance on Friday at Education City Stadium, it seemed a 1-1 tie was the best South Korea could do against the Selecao.
In another match in Group H, Uruguay defeated Ghana 2-0, and as a result, La Celeste will be joining Portugal in the next round.
However, Son placed Fernando Santos' team under pressure with a determined run at the centre of the Portuguese defence in stoppage time of the second half. The Tottenham forward then expertly threaded a pass through the legs of a defender for Hwang Hee-chan to cling onto.
Paulo Bento, the head coach of South Korea, stared on in confusion from the stands as Hwang boldly surged past Diogo Costa to cause havoc among the team's players, substitutes, and staff. Bento had received a red card the previous match.
It was a lengthy wait for Son as South Korea managed to win and were then left with an anxious six-minute wait for the other game to end. Uruguay duly failed to score the additional two goals necessary.
Son told reporters afterward, "I'll say it was the longest six minutes of my life, but in the huddle [on the pitch] we were incredibly enthusiastic.
"Look, we deserve this; it's well deserved," the guys were saying. And I responded, "I'm f****** proud of this team regardless of what happens, even if Uruguay scores more goals."
"I said that, you know. This crew contributed everything, and I'm incredibly proud of them. When I was certain that we would pass, everyone just waited. But six minutes is a long time.
South Korea and Son experienced grief at the same point in Russia 2018 four years prior.
A 3-0 victory for Sweden against Mexico meant South Korea did not advance to the round of 16, despite their victory over Germany on matchday three, which confirmed the elimination of the previous champions.
Son, though, was so overcome with elation after their victory on Friday that disappointment did not even enter his mind.
Naturally, I believe there were similar occasions. We defeated Germany 2-0, and if Mexico won their match, we would have advanced. However, this time, things turned out differently.
"We were awaiting additional results, but I was so pleased and gratified that I forgot about four years ago. How shall I put it? I felt incredibly proud and delighted.
Son was eager to honour the entire team on what was a memorable day for everyone, even those who did not play. The Taeguk Warriors' comeback against Portugal was evidence of their character, and Son was eager to pay tribute to the entire squad.
Because the guys have been at the camp for more than a month, he continued, "we are spending more time together than with friends and family.
"I believe that we are very close, and I'm really thankful that those who did not participate were undoubtedly quite disappointed, but they did not express it.
On the bench, they gave all to help us. I think it makes a huge difference to work as a team rather than just going our separate ways, so I'm extremely grateful and happy to be in charge of this team.
The next opponent for South Korea will be whoever wins Group G; Brazil is likely to be that team.