[3][4] Hansack came back to Major League Baseball when he signed with the Red Sox on December 9, 2005.

He played for the Red Sox Double-A team, the Portland Sea Dogs where he posted an 8–7 record with a 3.26 ERA in 31 games (18 starts).

[5] Hansack made his Major League debut against the Toronto Blue Jays on September 23, 2006, pitching 51⁄3 innings and allowing three runs while recording two strikeouts to earn the loss.

Hansack faced fifteen batters, walking only Fernando Tatís, who was then retired in a double play.

[8] Hansack was re-signed as a minor league free agent by the Red Sox on January 25, 2010.