Setting the scene
The American and National Leagues had operated as rivals until a peace agreement in 1903 set up a postseason showdown between each league's pennant winners.
What happened
The first modern World Series was played in October 1903 as a best-of-nine series; the Boston Americans (later Red Sox) defeated the Pittsburgh Pirates five games to three.
Why it still matters
That fall classic established baseball's October ritual and proved interleague postseason play could draw national attention. Memorable detail: Pirates star Honus Wagner struggled at the plate, batting just .222 in the series.
Background
The best-of-nine format established baseball's fall classic.