Despite his struggles, Affeldt was named to the Giants' playoff roster. Affeldt made his first playoff appearance for the Giants in Game 2 of the 2010 NLCS against Philadelphia. He struck out one batter and intentionally walked another one, but Santiago Casilla allowed him to score as the Giants lost 6–1. Affeldt faced (and retired) one batter in Game 5, but the Phillies won that game 4–2. In Game 6, Affeldt entered the game in the third inning with runners on first and second and nobody out after starting pitcher Jonathan Sánchez was taken out early. He pitched two hitless, scoreless innings, and the Giants won the game 3–2 to advance to the World Series. Affeldt pitched in two games in the World Series, which the Giants won in five games to give Affeldt his first World Series ring.