The next season, Whiteside started the year at Fresno again, batting .241 with 28 hits, six home runs, and 24 RBI in 34 games (116 at bats). However, after an elbow injury prevented Pablo Sandoval from catching, the Giants called up Whiteside to be the backup catcher for Bengie Molina on May 24, 2009. The same day, he played his first major league game in four years (and his first for a National League team). He finished the game with a hit and an RBI in three at-bats. Matt Cain said of Whiteside, "He's been great. He's a guy who definitely takes advantage of his days in between, when he's not catching, and asking what guys threw in situations and what the pitches were, so he isn't thrown into the fire the days he's starting. Even if he doesn't see a team, he's still figuring out how guys got them out. He's definitely always learning." On July 10, 2009, Molina was scheduled to catch, but was unable to because he went to see his wife, who was having a baby. Whiteside caught in his place, and Jonathan Sánchez, starting in place of the injured Randy Johnson, threw a no-hitter against the San Diego Padres. When asked if he thought it was more unlikely for Sánchez to throw a no-hitter or for him to catch it, he said, "Probably me catching one." He hit a grand slam, his first Major League home run, against Brian Moehler of the Houston Astros in a 10–6 Giants' victory on August 5, 2009. He joined Bobby Bonds, Dave Kingman, Brandon Crawford and Brian Dallimore as the only Giants to hit a grand slam for their first home run. He finished the year with 29 hits in 49 games (126 at-bats), two home runs, and 13 RBI. Defensively, he posted a .993 fielding percentage while catching 39% of attempted base stealers.