According to someone (reliable source? :lol, Guillermo has been playing stunning tennis in practice, you wouldn't guess that he'd been sidelined for so long. But matches are an entirely different scenario.
If he can get his serve to land in the box consistently, then naturally he's the favourite.
I'm sure, even when he was hitting all those DFs, he was never doing it in practise. It's a mental problem with Coria and he needs to feel more relaxed playing official ATP maches. If this event were still Round Robin, I would fancy his chances a little better.