The 2021 American League Division Series were the two best-of-five-games series in Major League Baseball (MLB) that determined the participating teams of the 2021 American League Championship Series. The three divisional winners, seeded first through third, and a fourth team—determined by the AL Wild Card Game—played in two series. These matchups were: * (1) Tampa Bay Rays (AL East champions) vs. (4) Boston Red Sox (Wild Card Game winner): Red Sox win series 3–1. * (2) Houston Astros (AL West champions) vs. (3) Chicago White Sox (AL Central champions): Astros win series 3–1.