He rose through the ranks fairly quickly. With Low Class-A Lowell in 2000, he was 5-2 with a 2.60 ERA. He struck out 93 and walked just 20 in 72.2 innings. Across two levels in 2001, he was 8-4 with a 1.90 ERA. He had a 3.75 K/BB rate and a 9.9 K/9.
At the trading deadline in 2002, Song was packaged along with fellow Korean Sun-Woo Kim to Montreal for Cliff Floyd. Duquette was not very good at building up and retaining a decent farm system and wanted another bat for the stretch run. Ultimately the move did not pay off. Floyd was a good hitter, but Boston still fell short of the postseason and allowed Floyd to walk after the season.
Song pitched in just one game in Montreal's system the rest of the way in 2002. He had a good season in 2003, making it to Triple A for the first time and going 12-4 with a 3.08 ERA. Unfortunately, that was the last of his success. His career stalled after that due to injuries and ineffectiveness. In 2004 he was 4-2 with a 4.78 ERA over three levels. He had a little more success in 2005, but was moving backwards. He last appeared in the U.S. in 2006 in the Royals system. After that season he returned to Korea where he has pitched ever since. He is still active in Korea.