Son Heung-min reacts to a 1-0 loss to South Africa in the teams' Group A match at the FIFA World Cup at Estadio Monterrey in Guadalupe, Mexico, June 24. Yonhap

GUADALUPE, Mexico — For the first time in his international career that started in 2010, Son Heung-min began a World Cup match on the bench Wednesday. The veteran admitted to feeling helpless, as Korea struggled to generate much offense in the first half against South Africa in their final Group A match in northeastern Mexico.

Son was subbed in at the start of the second half, with the match still scoreless. But then South Africa scored in the 63rd minute and hung on to win by 1-0 to book their first-ever knockout spot.

Korea, relegated to third place, now must wait for the rest of the group stage to play out to see if they will be among the eight best third-place teams to qualify for the knockouts.

"It's so frustrating that the match didn't go the way we wanted it to, and we as players are obviously very disappointed," Son said. "I feel sorry to my teammates that I didn't give them much help on the pitch."