Turnbull will start Sunday's series finale against the Reds.
Matthew Boyd and Ivan Nova will take the mound for the first two games of the season, while Turnbull opens the season as the No. 3 starter. The 27-year-old completed his first full season in the majors last season and had a 4.61 ERA, 1.44 WHIP and 146:59 K:BB over 148.1 innings.