Sure he could. Del Potro has never been the same player since his injuries. He's a really good player, but he's prone to mentally checking out time and again and he just doesn't dominate like a player with his skill set should. He has looked good this tournament, but not great over the course of each set. Roddick gets an advantage playing at night where the weather won't wear him down as much and the crowd will be electric again. That really is a massive plus because Delpo is the kind of idiot who will let the crowd's involvement bother him when it should have no effect. Roddick will have the play probably his best match of the year to win, but Del Potro is certainly not unbeatable. I think for Roddick to entertain any shot of winning, he's got to get off to a quick start.
In the end, I think Del Potro probably will win - but it's certainly no where close to a lock.
I don't see how he does though, honestly. It seems like Del Potro makes alot less unforced errors...he's not gonna give away points like Tomic and Fognini...even if Roddick's serve is totally on point, it is still going to be pretty hard for him to break Del Potro.