During the 2018 Red Sox season, Pomeranz made his first start on April 20, after beginning the season on the disabled list due to a flexor strain. Through the end of May, his record was 1–3 with a 6.81 ERA. On June 5, he was placed on the disabled list due to left biceps tendinitis; he was activated on July 24 as a relief pitcher. He remained in the bullpen for the remainder of the season, finishing at 2–6 with a 6.08 ERA in 26 games (11 starts) for Boston. Pomeranz was initially not included on Boston's postseason roster, but was added for the World Series in place of Brandon Workman. Although Pomeranz did not pitch in the World Series, the Red Sox beat the Los Angeles Dodgers in five games, making Pomeranz a World Series champion for the first time in his career.