There's plenty of credit to go around, but the most important factor was that right from the chute, you could see that Roy Halladay had great life and good sink.
Beerleaguer: Halladay was never straight with a single pitch. He lived on the outside corners, and home plate umpire Mike DiMuro was happy to oblige. DiMuro established a liberal strikezone early and stayed consistent with it; once this game moved into the later stages, DiMuro's eyes must have been as wide as golf balls. Early on, Doc ran a number of three-ball counts and nearly hit Jorge Cantu, coming about five centimeters from clipping his uniform. Luckily, he was hitting the flat side of a dime and made easy work of the late innings. He struck out 11 and almost none of the balls hit were hit hard.
Afterward, Doc credited his handler, Carlos Ruiz, who gains entry into an elite club for having called a perfect game, only the 20th time one has occurred in baseball history. Halladay said that as soon as he reached the sixth, he followed Chooch's lead, so the catcher's role cannot be overstated.
Credit Charlie Manuel for going with the glove of Juan Castro over his allegiance to Greg Dobbs against a right-handed pitcher. Castro became the defensive star of the game, making three very good plays and the play of the game on a one-hop bullet to his left. Fellow reservist Wilson Valdez, who scored the game's only run, also stepped up at short by gunning down fleet-footed Cameron Maybin.
The most amazing part is that the dreadful offense, quite fittingly, gets the bare minimum amount of credit as the game's only run was unearned. But at least they scored.