In 2002, Sandoval was signed by the San Francisco Giants. Sandoval worked his way through the minor leagues and debuted with the Giants in 2008, batting .345 in 41 games. Capable of playing first base, third base, and catcher, he became the Giants' starting third baseman in 2009, ceasing to catch that year and playing first base only occasionally. In 2009, Sandoval finished second in All-Star Final Vote balloting, batting .330 with 25 home runs and 90 runs batted in (RBIs) in his first full season in the majors. However, Sandoval struggled in 2010 and was benched during the playoffs for the 2010 World Series, which the Giants won. He lost weight before 2011 and hit .315 with 23 home runs in 117 games. Injuries limited Sandoval to 108 games in 2012, but he was selected to his second-straight All-Star Game. Then, in Game 1 of the 2012 World Series, Sandoval joined Babe Ruth, Reggie Jackson, and Albert Pujols as the only players to hit three home runs in a World Series Game. For his contributions, Sandoval was named the World Series Most Valuable Player, as the Giants swept the Detroit Tigers. In 2013, he appeared in 141 games, batting .278, with 14 home runs, and 79 RBIs.