Martinez finished the 2018 season with 43 home runs and a career high 130 RBIs, which led MLB. He led the Red Sox in home runs, RBIs, and hits. In Game 1 of the ALDS, Martinez hit a three-run home run in the first inning off of New York starter J. A. Happ; Boston would win the game 5–4. In Game 5 of the ALCS, Martinez hit a solo home run off of Houston starter Justin Verlander; Boston won the game, 4–1, and clinched a berth in the World Series. In Game 5 of the World Series, Martinez hit a home run in the seventh inning to increase the Red Sox lead to 4–1. The Red Sox went on to win the game, capturing their ninth World Series title.