In what was a de facto, winner-takes-all knockout encounter for second spot in Pool C behind Japan, both sides knew runs on the board would be vital to see them head to the USA.
And it was the Koreans who struck first. Moon sent a two-run no-doubt shot 430 feet into the stands in the second inning to spark his side into life.
An inning later, it was Lee Jung-Hoo who would be their inspiration. He hit a sharp line drive into centre field to score Jahmai Jones, before Moon cashed in Lee to make it 4-0.
Australia's bat had gone quiet, and they remained scoreless midway through the game. Korea were now rolling, adding run number five in the fifth as Moon continued his fine day at the plate with his fourth RBI. He singled into left field, Ahn Hyun-Min, to all but kill the game off.
Robbie Glendenning would get his team on the board with a home run, but it looked too little, too late for the Australians, as the sides would trade runs in the latter stages, but South Korea held their nerve to close out the contest and secure a last-eight spot.
They are now likely to face the Dominican Republic in the quarter-finals.