In 2009, he had the best high school season, posting a 1.13 ERA and allowing only 8 earned runs in 63 innings pitched.

In April, Moon led his team to win the 2009 Golden Lion Flag National Championship, hurling 7.2 shutout innings in the final game, and was named MVP of the tournament.

In the championship, he had an excellent performance, going 2–0 with a 0.77 ERA and allowing only 7 hits in 11.2 innings while striking out 16.

He made his pro league debut on May 8 against the Hanwha Eagles at Mokdong Baseball Stadium, coming from the bullpen and tossing one scoreless inning of one-hit ball.

On the other hand, Kim Sung-hyun, a former teammate, was convicted of match fixing while with the Nexen Heroes but was later released after concealing this fact and transferring to the LG Twins.