Coach Huh Jung-moo said the players had overcome their disappointment from 24 hours earlier and were now focussed on their final Group B meeting with Nigeria in Durban on Tuesday.
If South Korea win, and Argentina top the group by beating Greece, they will join the South Americans in the second round and a likely meeting with Mexico or Uruguay.
"We are not depressed or too disappointed this morning," he said.
"We felt that the winnable games for us (in the group) would be against Greece and Nigeria and, now, the Nigeria game is very important.
"Everyone was disappointed last night, but in the dining room this morning there was a good mood. I am sure we will be ready. We will be bit more focussed, too, I hope.
"They will be without (Sani) Kaita, but they have a lot of other strong players and it will be hard," he said.
"They have very talented players, but very different from those of Argentina or Greece. We will attack, but this time we will not leave the back door open. We must be more tenacious."
South Korea won their opening match against Greece 2-0. They lie second behind Argentina with the Greeks on three points. Nigeria have been beaten by both Argentina and Greece.
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