With a late goal yet again, Belgium made the difference in the 78th minute when defender Jan Vertonghen followed up a shot from teenage striker Divock Origi and tapped in the rebound past goalkeeper Kim Seung-gyu.
''We knew all games were going to be tough,'' said Belgium coach Marc Wilmots. ''But even with 10 men, we still pushed forward. These guys are really hungry.''
After three narrow victories and precious little beautiful play, Belgium will now play the United States in Salvador on Tuesday.
''Mission accomplished,'' said Wimots.
They never came close.
''All of our players did their utmost. They gave it their all but I think that it was my shortcoming, my failing as a coach that caused this result,'' said coach Hong Myung-Bo.
The former captain of the 2002 team which reached the semifinals did not offer his resignation, though.
South Korea did not go without a strong fight, landing the ball on Belgium's crossbar on the hour-mark and testing standout goalie Thibaut Courtois with several shots afterward. Yet even with a man up, the Koreans could never pressure Belgium enough to find an opening and paid the price.
For scorer Vertonghen it was a bit of redemption after he caused the penalty against Algeria in the opener which forced Belgium into late histrionics to come back and claw out a 2-1 victory.
''I really felt bad after that but now only joy is left,'' he said.
Belgium promised to play with flair in this tournament but is proving that it's still a master at grinding out results.
''It gives us so much confidence to get those nine points with only 10 men and prepare for the Americans in that mood,'' Vertonghen said.
Having a goalie like Courtois does make it easier, especially as its defense was missing injured starters Vincent Kompany and Thomas Vermaelen. But the Belgians also proved they sorely lacked the creative skills of Kevin De Bruyne and Eden Hazard, who were on the bench from the start.
On the hour mark, South Korea came closest to scoring when Son Heung-min saw a cross float right onto the crossbar beyond the reach of Courtois.
Belgium fielded four World Cup newcomers, but was reduced to three in the 45th minute when Steven Defour planted his studs, leg outstretched, into the shin of Kim Shin-wook. Australian referee Benjamin Williams didn't hesitate to pull out the red card.
Earlier, the South Koreans almost scored around the half-hour mark. First, a long-distance drive from Ki Sung-yeung forced Courtois into a great diving save and, one minute later, Defour kicked a ball off the line in another goalmouth scramble.
Mertens could have lifted the pressure off Belgium in the 25th minute he was left wide open eight meters out. He skied the ball over, immediately opening his mouth in disbelief at having missed such a chance.
In the second half, South Korea brought on a second full striker in Lee Keun-ho for even more pressure.
The Asians created a flurry of chances early in the second half, but either Courtois showed his class or the South Koreans lacked any precision.
South Korea: Kim Seung-gyu; Lee Yong, Kim Young-gwon, Hong Jeong-ho, Yun Suk-young; Lee Chung-yong, Han Kook-young (Lee Keun-ho, 46th), Ki Sung-yueng, Son Heung-min (Ji Dong-won, 73rd); Koo Ja-cheol, Kim Shin-wook (Kim Bo-kyung, 66th).
Belgium: Thibaut Courtois; Anthony Vanden Borre, Daniel Van Buyten, Nicolas Lombaerts, Jan Vertonghen; Steven Defour, Moussa Dembele, Dries Mertens (Divock Origi, 60th), Marouane Fellaini, Adnan Januzaj (Nacer Chadli, 60th); Kevin Mirallas (Eden Hazard, 88th).
Follow Raf Casert on Twitter at https://www.twitter.com/rcasert
- Sports & Recreation
- South Korea
- Jan Vertonghen
- Thibaut Courtois
- Divock Origi