A goal in each half from Lee Jung Seon helped Korea beat Great Britain's men's hockey team's 3-2, ending their hopes of a second win in a row.
Lee was on target after 15 minutes but Danny Hall levelled matters early in the second half to give GB hope.
But Korea regained the lead through Yeo Woon Kong before another equaliser, this time from Niall Stott.
GB goalkeeper Simon Mason pulled off some superb saves but could do nothing to stop Lee three minutes from time.
GB tried to put Korea under pressure in the closing seconds, forcing two penalty corners, but they were unable to make them count against the silver medallists from Sydney four years ago
"The end was heart-breaking," admitted coach Jason Lee, who had seen his side beat Egypt in their opening game on Sunday.
"But I am proud the way the boys responded in adversity. They showed character when the chips were down."