South Korea fell 1-0 to Peru in a friendly on Friday, with the hosts missing their talisman Son Heung-min and top defender Kim Min-jae.
Bryan Reyna scored the only goal of the match in the 11th minute in Busan as Tottenham Hotspur star Son, recovering from a recent sports hernia surgery, watched from the bench.
Centre-back Kim, who won the Serie A title with Napoli, is completing his mandatory South Korean military training this month.
His absence was felt by the hosts when their defence was caught watching the ball as an unmarked Reyna scored from a Paolo Guerrero pass.
Peru nearly doubled their lead in the 19th minute when Guerrero's effort from a Reyna cross went just wide.
South Korea's first real chance came in the 33rd minute when Mallorca's Lee Kang-in shot from the edge of the box and forced Peruvian keeper Pedro Gallese to make his first save of the evening.
South Korea, still winless under recently appointed manager Jurgen Klinsmann, ramped up the pressure in the second half.
Oh Hyeon-gyu found himself one-on-one with Gallese during a counterattack just past the hour mark but failed to score.
Lee Kang-in and substitute Cho Gue-sung later failed to make their headers count.
Cho got another opportunity in the 89th minute but sent his header high and wide from a corner.
Klinsmann and South Korea will next face El Salvador on Tuesday.