David Ortiz — 2004 ALCS Against the Yankees

David Ortiz's walk-off hits in Games 4 and 5 of the 2004 ALCS engineered the most improbable comeback in baseball postseason history, erasing a 3-0 deficit against the Yankees. His Game 4 walk-off homer ended a 12-inning marathon, and his Game 5 single won it in the 14th — two clutch hits separated by 24 hours. Both hits produced a 100% win probability swing, a feat unmatched by any other player in a single series.