Where are you getting your stats from? We are 68 in pass defense. Not saying that we're world beaters on the defensive side, but theres kind of a difference between 68 and 117.
One thing our defense has been pretty good at is creating takeaways. I wouldn't be surprised to see this play a major part.
Look also at red zone play. Our defense has been better here also.
Duke is also 111th in sacks allowed this year. This, in my opinion, is the biggest fault with our defense. Our inability to get to quarterback allowed the receivers to have an extra 3-5 seconds. These boys have to step up.
I know people think we don't match up well because they're a great passing team, but if you look a little closer I feel like this game is more for the taking than most realize.