Hwang Hee-Chan's stoppage time winner has sent South Korea into the World Cup Round of 16 for the first time since 2010.
His late goal handed his nation a 2-1 victory over Portugal, meaning the Taegeuk Warriors finished second in Group H.
Hwang's goal came after Kim Young-Gwon had equalised for South Korea midway through the first half, cancelling out Ricardo Horta's early opener.
Celebrations were held inside the Education City Stadium, as South Korea's future depended on the outcome of Uruguay's clash with Ghana.
With Uruguay 2-0 up, a third would have sent them into the last 16, while two Ghana goals would see the Black Stars advance.
Neither side could alter the outcome, allowing South Korea to progress to the next round in the most dramatic fashion.
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Story of the match
South Korea made three changes to the side that lost to Ghana on Monday.
Kim Min-Jae was not deemed fit enough to start, while Kwon Chang-Hoon and Jeong Woo-Yeong dropped to the bench. Lee Kang-In and Lee Jae-Sung came into the midfield with Young-Gwon filled in at the back.
Head coach Paulo Bento was serving a touchline ban after his red card on Monday. Assistant coach Sergio Costa filled in.
Portugal were also heavily rotated, making six changes from their win over Uruguay.
Nuno Mendes missed out through injury, while key players such as Bernardo Silva, Ruben Dias and Bruno Fernandes dropped to the bench.
Fernando Santos handed a World Cup debut to Horta, as well as 19-year-old centre half Antonio Silva who was playing in just his 19th professional game.
Portugal started the game on the front foot, taking the lead after just five minutes.
Pepe's long ball over the defence found the run of Diogo Dalot.
The Manchester United man headed inside and dragged the ball back for the onrushing Horta to fire home from inside the six-yard box.
Santos' side looked to keep hold of possession, playing a low-energy game that would keep their players fresh for Tuesday's Round of 16 match.
Their passive play would cost them as South Korea equalised in the first half.
Kang-In's in-swinging corner deflected off the back of Cristiano Ronaldo and fell to Young-Gwon.
The centre half swung his left foot at the ball and managed to beat an outstretched Diogo Costa.
Portugal had the better of the remaining first half minutes, yet failed to create any significant chances.
Their best chance to retake the lead fell to their main man.
Vitinha's long range effort was saved by Kim Seung-Gyu, with Ronaldo following in with a diving header that he somehow fired wide of the goal.
The sides went in level at the break, with neither looking threatening in the final third.
With 25 minutes to go, assistant coach Costa introduced Hwang.
The Wolves man had not yet made an appearance in this year's tournament due to injury.
The winger instantly injected life into the game, driving at a tiring Portuguese defence before playing in Son Heung-Min, but the Tottenham forward failed to test goalkeeper Costa.
Portugal made five second half substitutions, seemingly taking control of a lacklustre game with an injection of energy.
Santos' side won a corner as the clock ticked over into stoppage time, sending men forwards in hope of maintaining their perfect group stage record.
A poor corner was cleared to the feet of Son, with the winger driving forwards at pace.
As he entered the final third, he split the defence with a perfect ball onto the right foot of Hwang.
All fours nations held their breath, awaiting a group defining shot.
The 26-year-old was the calmest man in Qatar, slotting the ball into the bottom corner as bedlam ensued.
South Korea rose from the foot of the table, joining their Portuguese opponents in the top two.
Referee Facundo Tello blew for full time, but the party could not start yet.
All attention switched to the Al Janoub Stadium, where one Uruguay goal or a Ghanaian comeback would see South Korea eliminated.
Despite a frantic end to the game, neither side managed to change the outcome as South Korean celebrations begun.
Both Portugal and South Korea will find out their next opponents later tonight.
Both will face sides from Group G, with Brazil and Switzerland currently in the qualification driving seat.
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Player of the match
Looking back through World Cup history, it would be hard to find anyone who had played so few minutes, yet made such an important contribution to the tournament.
Hwang Hee-Chan's involvement in today's game will go down in South Korean history, as his nation reach the last 16 for just the third time.
The winger looked lively after his spell on the side-line, adding much needed pace and emphasis to a dwindling South Korean attack.
Hwang will be hoping to use his goal as motivation to kick start his season for both club and country.