On September 1, 2012, the Yankees promoted Núñez from Triple-A and manager Joe Girardi placed him into the starting lineup against the Baltimore Orioles for that day. He finished the regular season with a .292 batting average in 82 at-bats. Though he was left off of the Yankees' postseason roster for the 2012 American League Championship Series, he was added to the roster when Jeter suffered a fractured ankle. In Game 3 of the 2012 ALCS, Núñez hit his first career postseason home run off of Tigers pitcher Justin Verlander. The Yankees lost the series to the Tigers in a 4-game sweep.