The 2021 Major League Baseball postseason ran from October 5 to November 2, marking the final year of the 10-team playoff format before the league expanded to 12 teams in 2022. The tournament featured dramatic wild-card games, including the Boston Red Sox defeating the New York Yankees 6–2 and the Los Angeles Dodgers beating the St. Louis Cardinals on a walk-off two-run homer by Chris Taylor. In the ALDS, the Red Sox upset the defending champion Tampa Bay Rays in four games, highlighted by a 13-inning walk-off win in Game 3. The San Francisco Giants posted the best regular-season record (107–55), but it was the Atlanta Braves who captured the World Series, defeating the Houston Astros in six games—their first championship since 1995 and fourth overall. Notably, this remains the most recent postseason appearance for the Chicago White Sox as of 2026, and the year featured at least three 100-win teams for the fourth time in five seasons.