Just to the left of Atria's on the Roberto Clemente Bridge side of PNC Park is where you'll find The Diamond Pizza.
Not only do they have really good pizza, the cheese is especially good, but you can enter the park there as well. Never a line. Friendly ticket taker and bag search person greet you at the door, scan your ticket and provide a program along with any promotional items for the game.
Once inside, order by the slice, grab a beer if that's your pleasure and watch the game on either of the TVs before going to your seats. Another bonus, restrooms are just outside the restaurant as you enter the left field corridor.
Like most pizza/sandwich shops, this one can be hopping. No frills in the service, mustard working folks trying to make good food for the money. And they do.