The biggest play of the game was the missed PI in the first half that resulted in an INT and a return for a TD. That was a free 7 points in a game that went to double OT. What was bad about this is that during the course of the game, Dierdorf would get worked up about how the referees spotted the ball various times when Harbaugh was upset. Sorry but this doesn't come close to the missed PI that resulted in 7 points.
But I agree with the criticism of Perreira here. That guys is a worhless piece of ****. He's everything that's wrong about the NFL now.