On July 31, 2009, Martinez was traded to the Boston Red Sox for Justin Masterson, Nick Hagadone, and Bryan Price. Martinez would regularly play between first base and catcher, catching usually for the younger pitchers within the rotation, with some of the veteran starting pitchers opting for Red Sox captain Jason Varitek. On August 26, 2009, Martinez caught for Tim Wakefield, the Red Sox's veteran knuckleball pitcher. It was the first time Martinez had ever caught the knuckleball, and for seven innings he not once let a wild pitch or passed ball go by him. Ironically enough, prior to Martinez being traded to the Red Sox, he was set to be Wakefield's catcher had he been called on to pitch in the 2009 All-Star Game. Martinez hit his first career grand slam against, ironically, the Cleveland Indians on 10/3/09.