Belgium must prepare for their last-16 match against the USA without the services of Steven Defour after the midfielder was shown a straight red card in the victory over South Korea.
Tottenham defender Jan Vertonghen pounced in the last 15 minutes to make sure Belgium sewed up Group H with a perfect record but Defour's transgression, for a dangerous tackle on Shin-Wook Kim just before half time, marred the win.
Nonetheless Belgium's qualification marks a remarkable turnaround in fortunes in their first World Cup since 2002, as South Korea head home with just a point against Russia – while Algeria qualify in second – to show for their efforts.
With Chelsea target man Romelu Lukaku dropped to the bench and Eden Hazard rested, Belgium decided to line up without a recognised striker.
It heralded Manchester United starlet Adnan Januzaj's first World Cup start for his country and together with Everton's Kevin Mirallas, who was furthest up field for Belgium, looked lively early on.
But South Korea – needing a win by two goals to stand any chance of qualifying – showed plenty of endeavour themselves, culminating in Ja-Cheol Koo going down in the box after a hefty tackle from Tottenham midfielder Moussa Dembele.
The challenge was deemed a fair one and before long Belgium were appealing for their own penalty, as Young-Gwon Kim was judged to have fairly shielded the ball from right-back Anthony Vanden Borre in the area.
Midway through the first half, clever work from Mirallas saw the winger wriggle free on the right to whip in a dangerous cross – but nobody was there to apply a simple tap-in.
Moments later however he carved out a glorious chance for Dries Mertens who, from eight yards out, blazed his shot over the crossbar.
On the half-hour mark South Korea fired a warning shot across the bows after Sung-Yong Ki forced Chelsea keeper Thibaut Courtois into a fine save from long-range.
Favourites Belgium continued to only flicker brightly in patches and on the stroke of half time, were firmly on the backfoot because of Defour's rashness.
The 26-year-old raked his studs across Shin-Wook Kim in a wild challenge and was immediately shown a red card by referee Benjamin Williams.
Buoyed on, South Korea seized the initiative after the break as a vigilant Courtois raced out to nip the ball from the feet of Keun-Ho Lee.
Down at the other end another penalty shout was waved away after Januzaj played in United teammate Marouane Fellaini, who appeared to trip under the attentions of Jeong-Ho Hong.
Mertens then went close with a rasping right-footed effort from 25 yards out, which Seung-Gyu Kim neatly palmed away.
And in the face of mounting pressure, the Koreans finally buckled when Kim parried a shot from substitute Divock Origi – who scored Belgium's winner against Russia – into the path of Vertonghen.
The left-back was deemed to have stayed onside by the narrowest of margins and still Belgium pressed with sub Eden Hazard going close in the dying stages in a lively cameo.
South Korea then nearly signed off from the World Cup in style through Chung-Yong Lee, but Courtois was equal to the Bolton winger's shot.
Attendance: 61,397
Referee: Benjamin Williams (Australia)
South Korea 0
Belgium 1
Vertonghen 77
South Korea: (4-2-3-1): Seung-Gyu Kim, Yong Lee, Suk-Young Yoon, Young-Gwon Kim, Jeong-Ho Hong, Kook-Young Han (Keun-Ho Lee, 46), Ja-Cheol Koo, Sung-Yong Ki, Chung-Yong Lee, Heung-Min Son (Dong-Won Ji, 73), Shin-Wook Kim (Bo-Kyung Kim, 66)
Subs not used: Sung-Ryong Jung, Beom-Young Lee, Tae-Hwi Kwak, Seok-Ho Hwang, Joo-Ho Park, Chang-Soo Kim, Jong-Woo Park, Dae-Sung Ha, Chu-Young Park
Belgium: Courtois, Vanden Borre, Van Buyten, Lombaerts, Vertonghen, Fellaini, Defour, Dembele, Mertens (Origi, 60), Mirallas (Hazard, 87), Januzaj (Chadli, 60)
Subs not used: Bossut, Mignolet, Alderweireld, Ciman, Witsel, De Bruyne, Lukaku
