 Duncan made his major league debut on July 20, 2007, as the designated hitter against the Tampa Bay Devil Rays, and recorded his first career hit and RBI.The next day, he hit his first major league home run against the Devil Rays, and the following day had his first multi-home run game, going deep twice in front of the Yankee Stadium crowd.Duncan later hit his fourth Major League home run at Yankee Stadium on July 31, 2007 against the Chicago White Sox.