In the final game of the best-of-three 1951 National League tie-breaker series at the Polo Grounds against the crosstown rival New York Giants, Branca entered the game in relief of Don Newcombe in the bottom of the ninth inning with one out and Whitey Lockman on second base and pinch runner Clint Hartung on third base and surrendered a walk-off home run, which became known as the "Shot Heard 'Round the World" to Bobby Thomson, giving the Giants the pennant. Prior to facing Thomson, Branca had been warming up in the bullpen with Carl Erskine. Dodgers coach Clyde Sukeforth noticed that Erskine was bouncing several curveballs in the dirt and instructed manager Charlie Dressen to call on Branca—this despite Thomson having homered off Branca in Game 1.