South Korea coach Hong Myung-bo admits errors were made in their preparation in the build-up to their defeat to Algeria but stopped short of saying they underestimated their Group H rivals.
Algeria, having narrowly lost to Belgium in their opening game, raced into a 3-0 half-time lead through goals from Islam Slimani, Rafik Halliche and Abdelmoumene Djabou.
Song Heung-min and Koo Ja-cheol gave South Korea hope in the second half but Yacine Brahimi scored in between their efforts to seal a 4-2 win for Algeria, who had made five changes from the Belgium game to claim just their second victory in World Cup finals history.
South Korea had been the favourites going into the game having drawn with Russia in their first match and, following the result, Hong conceded his side must move on after a disappointing display.
"The result speaks for itself," he said.
"We made mistakes in our preparation and during the match, but we need to look ahead now. There were lapses in concentration, particularly in defensive areas and we didn't play to our usual standard."
Hong did refute claims South Korea assumed they would ease past their African opposition, with his side now needing other results to go their way if they are to get out of Group H.
"I must stress, we did not underestimate Algeria," he added.
"Their team was completely different than the one that played against Belgium. They played much better and deserved the win. Now we just need to move on. We will do our best until the end."
With a draw in Algeria's final group game against Russia in Curitiba likely to be enough for them to progress through the group, Slimani remains hopeful that a first appearance in the latter stages is something Vahid Halilhodzic's side can accomplish.
"It was brilliant to score for my team, it's a wonderful feeling," the Sporting striker said following his opening goal.
"I have to thank the coach for giving me the opportunity and I can say that all of the players gave everything for this win today. It's still our aim to reach the round of 16, we have a chance and I hope we'll achieve that."