Federer-DelPotro is sort of like Novak-DelPotro. It's just a very bad matchup for the big guy in general. It was bad in 2009 when he was at his peak and it hasn't gotten any better now that his backhand is so vulnerable.
Still, Del Potro is a great, great player and has the capability to beat anyone, including his bad matchups. On this surface, which is so fast, you give him a punchers chance. He needs a high percentage of first serves, and Roger needs to have a few mental lapses.
Still, I don't see it. Roger has been playing too well.