The 1999 American League Championship Series (ALCS) was a matchup between the East Division Champion New York Yankees (98–64) and the Wild Card Boston Red Sox (94–68). The Yankees had advanced to the Series after sweeping the West Division Champion Texas Rangers in the AL Division Series for the second consecutive year, and the Red Sox advanced by beating the Central Division Champion Cleveland Indians three games to two. The Yankees won the series four games to one and went on to win the World Series.

Both teams came into the series on a roll; New York had swept the Texas Rangers for the second straight year in the 1999 American League Division Series and Boston had come from two games down to defeat the Cleveland Indians in their division series. However, the Yankees won in five games. They would register their only postseason loss of the 1999 season in this series.

New York won the series, 4–1.

Wednesday, October 13, 1999, at Yankee Stadium (I) in Bronx, New York

Game 1 was a matchup between Kent Mercker and Orlando Hernández. The soon-to-be-named 1999 ALCS MVP got into trouble in the first two innings. After a leadoff single by José Offerman, John Valentin would reach on an error by Derek Jeter, scoring Offerman for the first run of the game in the first. Valentin would score on Brian Daubach's single to right. It looked like the Red Sox were ready to clobber the Yankees, but no more runs would score in the inning. Darren Lewis would score on an infield hit in the second to make it 3–0 Red Sox, but the Yankees' resilience showed itself in the bottom half. With Shane Spencer on first with two out, Scott Brosius slugged a home run to make it a one-run game. The duel continued into the seventh. With Derek Lowe now pitching, Brosius singled to lead off the inning. A sacrifice bunt by Chuck Knoblauch moved him into scoring position. Jeter would single to center and drive in Brosius to tie the game. Small ball helped the Yankees tie the game, but the long ball would win it in the bottom of the tenth. Rod Beck came on in relief and promptly gave up a leadoff homer to Bernie Williams to lose the game for the Red Sox. The Yankees had a one-game lead in the series.

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