1902: 103-36, .741; no postseason
1909: 110-42, .724, won World Series
Both the modern World Series and the 154-game schedule were a year away from being invented when the 1902 Pirates—led by Hall of Famers in star hitter Honus Wagner (pictured above), ace Jack Chesbro and manager/outfielder Fred Clarke—trounced the rest of the NL to the tune of a 103-36 record. Amazingly, the Bucs never lost more than two in a row en route to winning their second of three straight pennants by 27 1/2 games. Incidentally, it was owner Barney Dreyfus who conceived the idea of the World Series after this season, an extension of the peace treaty he had brokered with the two-year-old American League.
The Pirates went 91-49 the next year before losing to the Boston Americans (now Red Sox) in the World Series. Pittsburgh's first title came in 1909, when it finished 110-42 before handing Ty Cobb's Tigers their third straight World Series defeat, in seven games.