October 3, 1981: Montreal Expos clinch franchise's first playoff berth – Society for American Baseball Research

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Did expos fans abandon the Montreal franchise after the 1981 season and never really come back in large numbers ever again? - Quora

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Expos clinch playoff berth (1981)

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October 7, 1981: Expos win first MLB postseason game played outside U.S. – Society for American Baseball Research

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