The win kept South Korea's hopes of advancing out of Pool B play alive. Taiwan (2-0) leads the group while South Korea and the Netherlands are both 1-1. Australia (0-2) won't qualify for the second round.
Pool B wraps up play Tuesday with Taiwan playing South Korea and the Netherlands meeting Australia. The top two teams in the group move into the WBC second round.
Song (1-0) allowed two hits over four innings while walking two and striking out five. The South Korean bullpen allowed four hits the rest of the way.
The top four batters in the South Korean lineup combined for eight hits -- two more than the Australian team -- and six runs scored in handing Ryan Searle (0-1) the loss.
South Korea loaded the bases in the first inning with a walk, a double and another walk before Kim Hyun-soo singled in a pair of runs. A third run scored on a fielder's choice.
Lee Seung-yeop doubled home a run in the second that made the score 4-0. South Korea added runs in the seventh and ninth innings with Lee Dae-ho knocking in one and Jeong Choi the other.