Reduced to 10 men for over half the match, Belgium still beat South Korea 1-0 on Thursday to finish atop of Group H and eliminate the last Asian team from the World Cup.
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. And along with Iran, Japan and Australia, South Korea departed as the last team from the Asian federation, all in the first round.
Algeria finished second in the group after a 1-1 draw with Russia — a result that meant South Korea needed a four-goal win to advance.
While that never looked likely, 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 on a counterattack.
Belgium promised to play with flair in this tournament but is proving that it's still a master at grinding out results. 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.