In 2007, Komatsu was 1-0 with a 2.53 ERA in eight relief appearances, striking out 13 in 102⁄3 IP. He had a huge year in 2008, going 15-3 for a team that was otherwise under .500; he had a 2.51 ERA and allowed 134 hits in 1721⁄3 IP.
He finished third in the Pacific League in ERA and wins, behind Hisashi Iwakuma and Yu Darvish in both categories. His 151 strikeouts placed him 5th and was named Rookie of the Year that season, being a unanimous pick.