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http://www.Baseball-almanac.com/ws/wssweeps.shtml
The above link indicates World Series won 4 games to none. However, it also show 2 ties in the 1907 and 1922 World Series, so those were technically 5-game series, not 4.
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Since the beginning of World Series play in 1903 no team has won the Series after having lost the first three games.
This has been "accomplished" twice:
By the 1907, 1908, 1909 Detroit Tigers
1911, 1912, 1913 NY Giants
In the 100-plus years of World Series history, no team has ever won a world championship after losing the first three games.
In the history of the World Series, no team has lost the first three games and come back to win the remaining four games.