From May 8 through July 24, Affeldt had a twenty–eight inning scoreless streak. During the streak, on May 15, he struck out a season–high four batters in an 8–6 loss to the Mets. On May 31, he entered a game against St. Louis with runners on first and third and Albert Pujols on deck in the eighth, and he struck out Joe Thurston to end the inning and help the Giants win 5–3. The streak did not end until July 28, when Brandon Medders allowed one of Affeldt's runners to score in a game against Pittsburgh. On August 2, with runners on first and second with one out in the eighth inning against the Philadelphia Phillies, he retired Chase Utley and Ryan Howard to help the Giants win 7–3. He won the final game of the season against San Diego by pitching two scoreless innings as the Giants won 4–3 in ten innings. Affeldt finished the season with a career best 1.73 ERA in seventy–four games. He was named tenth on one writer's ballot for MVP voting, placing him in a tie for twenty–eighth on the list. On December 17, he won the This Year in Baseball Setup Man of the Year Award.