Meanwhile, Algeria secured its first-ever ticket to the round of 16 by drawing 1-1 against Russia in Curitiba.
Belgian captain Jan Vertonghen pounced on a rebound off goalkeeper Kim Seung-gyu to score in the 78th minute – the third game in a row that Belgium has scored the winner in the last 20 minutes.
Korea’s coach Hong Myung-bo made two changes to his previous lineups: Goalkeeper Kim Seung-gyu replaced Jung Sung-ryong, while Kim Shin-wook, who appeared in the second match with Algeria, started instead of struggling forward Park Chu-young.
Belgian coach Marc Wilmots, meanwhile, made seven changes, opting to give his younger players some time on the field ahead of the knockout round.
Mirallas passed to an unmarked Mertens on the edge of the area in the 34th minute, but his shot was off target.
Shortly after, defender Hong Jeong-ho received a yellow card for holding Belgium’s Mirallas. Mertens made the free kick, which goalkeeper Kim tipped over the crossbar.
Korea gained an advantage at the end of the first half when midfielder Steven Defour received a red card after smashing into Kim Shin-wook’s ankle in a tackle, leaving the Belgians to play the second half one man short.
Lee Keun-ho -- a substitute in the previous two games, who scored Korea’s lone goal against Russia -- brought a flair of energy to the front line in the second half, coming on for midfielder Han Kook-young to threaten the box several times.
Mirallas attacked with a low shot in the 58th minute, but Kim cleared it. The ball was passed to Son, who drove the ball down the right and hit a speculative ball to the far post that rattled the crossbar.
In the 78th minute, goalkeeper Kim blocked a shot by second-half Belgian substitute Divock Origi, but Vertonghen took advantage of the rebound and scored the lone goal of the game.
Star midfielder Eden Hazard came on for Mirallas with two minutes left, but the game was already won.
After the final whistle, defender Kim Young-gwon lay motionless in the grass near the Korean goal as the team took in its defeat. The Taeguk Warriors slowly made their rounds to the 61,000 spectators and bowed to its fans. Son Heung-min, in tears, was among the last of the team to leave the pitch.
The team returns to base camp in Foz do Iguacu on Friday morning to recover before returning to Korea.
Korea was the last Asian Football Confederation team to go home without a victory, with Japan, Iran and Australia having already left winless in the group stage.
At the top of Group H with nine points, Belgium moves on to play Group G’s second team, the U.S., in Salvador on July 1. Algeria, with four points, will play Germany in Porto Alegre on June 30.
By Elaine Ramirez, Korea Herald correspondent (email@example.com)