<Li> 2003 AL Championship Series: Yankees defeat Red Sox, 4--3 </Li> <Li> 2004 AL Championship Series: Red Sox defeat Yankees, 4--3 </Li> <P> The Yankees--Red Sox rivalry is a Major League Baseball (MLB) rivalry between the New York Yankees and Boston Red Sox . The two teams have competed in MLB's American League (AL) for over 100 seasons and have since developed one of the fiercest rivalries in American sports . In 1919, Red Sox owner Harry Frazee sold star player Babe Ruth to the Yankees, which was followed by an 86 - year period in which the Red Sox did not win a World Series . This led to the popularization of a superstition known as the "Curse of the Bambino", which was one of the most well - known aspects of the rivalry . </P> <P> The rivalry is often a heated subject of conversation, especially in the home region of both teams, the Northeastern United States . Until the 2014 season, every season's postseason had featured one or both of the AL East rivals since the inception of the wild card format and the resultant additional Division Series; they have faced each other in the AL Championship Series (ALCS) three times . The Yankees won twice, in 1999 and 2003; while the Red Sox won in 2004 . In addition, the teams have twice met in the last regular - season series of a season to decide the league title, in 1904 (when the Red Sox won) and 1949 (when the Yankees won). </P>

When did the red sox yankees rivalry began