McCullers will pitch the third game of the regular season, Chandler Rowe of the Houston Chronicle reports.
Astros manager Dusty Baker set the rotation for the first four games, and McCullers slots in for the third game, although he's viewed as the team's second-best starter. Zack Greinke will start Opening Day followed by Cristian Javier. McCullers, who is ready to go after throwing 90 pitches in a "B" game Wednesday, finished Grapefruit League play with two runs allowed on five hits and two walks while striking out 11 over seven innings.