A stolen base allowed and brain freeze by an infielder are going to be the difference. Amazing the pitching holds it close enough for those things to matter.
I've always thought that the best time to make the pitching change is after the 2nd out in a tough extended inning as it seems it's inevitable that the pitcher lets down after the 2nd out.
actually in a sense my bigger complaint about them playing Willi is the argument that he's playing because he can hit better than the alternative. I just don't believe he is even the better hitter.