Definitely the Pitt game. I thought when we were down 20-6 it was over and I was especially annoyed because i thought bringing in Tommy was what was going to cost us the game. Then once we tied it 20-20 i felt confident we'd win but when Cierre Wood fumbled i was certain it was over. I don't see how anyone before that Pitt fg didn't think we were going to lose. Even before that fg, in the first OT, i was scared stiff when Brindza was lining up for a fg and if he missed our season was over (keep in mind his previous kick he had missed an extra point).
The best moment of the season was the video of the stadium security guard jumping up and down in the endzone after the Pitt kicker missed that fg. I got goosebumps and started crying and finally felt like i could maybe move on from BC '93, the Bush Push, the Michigan State loss in '05, the Michigan State fake fg in '10, the Tulsa loss, the etc.
Next after the Pitt game, i would say when Tommy came in the Purdue game i was scared. Goodman made an incredible catch to bail him out. My gut is if that game were to have to OT we would've lost.
After that BYU had pretty nervous, even on that 3rd down call to Atkinson by the goalline I thought he wouldn't be able to get in.
The USC game i strangely wasn't as worried although looking back, I think if USC were to have gotten in the endzone on that drive, we would have lost unless we were able to run out the clock. We would've done 3 straight runs and if USC stopped us, they'd get the ball back with 2-3 minutes left needing just a fg to win and they'd throw bombs to Lee and Woods and probably get a pass interference call. I felt confidence our defense could prevent USC from a TD but if USC just needed a fg with a good kicker, we very well could have lost.