Man, that's a pretty close pitch to end the game there. Rizzo was smart to take the 3-1 pitch in that spot -- I'm not sure what he could have done with that pitch other than maybe break his bat -- and I think Duke has reason to be upset. Check out the PitchFX strike zone map:
The computers had the pitch in the strike zone, but home plate umpire Ron Kulpa thought it was too far inside, so ball four it is. And that's the ballgame.
The Cubs are now 72-41 on the season, the best record in baseball by five games. They have a very comfortable 13-game lead in the NL Central.