For months, I have been thinking very similarly about the Ohio State game: that it was turning out to be a curse in disguise. My reasons are slightly different than the other posters, but I don't disagree with any of the other opinions or observations.
I almost didn't watch that tOSU game real time because I was expecting a depressing and predictable failure. My hope was simply that they wouldn't get blown out. Was it going to be a repeat of the 2015 National Championship Game? Very likely. Then, much to mine and everyone else's surprise, they won and did so looking very solid. It certainly shocked press people and everyone else around the college football world. The way the Ducks won was as impressive as the mere fact that they pulled an upset.
I think one key to explaining that how they pulled off that great performance and then delivered so many subsequent let-downs is that in that game, the Ducks had NOTHING TO LOSE when they faced Ohio State. Everyone was expecting them to lose. There was less mental, performance pressure in that early season game because they just had nothing to lose. I have a little bit of coaching experience with high schoolers in soccer, and I think it holds true for any sport and any level of competition, that handling, processing, or dealing with the internal mental pressure of competition is as important as any other factor.
Success and expectations can create pressure to live up to a billing or ranking (or to achieve a lofty goal that is now suddenly more feasible). From that kind of pressure a multitude of dangers can ensue: mainly doubt, fear, and anxiety. The mental/emotional playing clarity that every athlete needs to perform at their optimum is a state of mind where the player is so utterly immersed in the game that they become, to borrow a phrase from Emerson, "the transparent eyeball." Most coaches make a lot of effort to defeat these mental distractions (we play one game at a time, or like when Mark Helfrich used to say, "we're loose"), but which coach actually succeeds is at it? The coach has to first apply it to himself. It is a test of character more than anything.
In sports, the higher you go, the more pressure is there, internally, within each player, as much as externally. I think about how often a professional soccer player misses or flubs a penalty kick or a free kick scoring opportunity. Those players are exponentially more skilled than anyone I coached, but they flub almost as often. Why? Because they live with vastly more pressure. Imagine an entire nation hating on you because you flubbed a free kick at a critical juncture in a world cup match (ask David Beckham), and that is just the external pressure.
In the case of the Ducks, I think there was a great deal of internal pressure, probably within each person in the entire organization, once they had that unexpected win at tOSU. Suddenly, they were one of the top teams in the nation. That's a lot to live up to... and it can paradoxically breed a current of complacency. The thoughts are, "We're #3 now; beating tOSU is what we do; and opposing teams will just fold up against us because none of them are as good as Ohio State. I prepared for tOSU with 'x' amount of effort, and that was good enough, so for a team ranked 35 lower than tOSU, I only have to prepare 'x-35' amount." Ok, probably no player will admit to thinking those things, but there had to have been a tendency to think that way. Some probably gave in more than others.
Here is one example of the potential negative impact of success: A coach, under the self-induced mental pressure to live up to expectations, can become risk averse and stingy with his substitution decisions and that can have a subtle yet insidious impact on the team culture. It can generate a win-at-all-costs attitude that undercuts other the coaching messages about "playing loose" and communicates pressure to the players on the field as well as to those who get subbed in. If you know you won't get subbed in as often, because we have to win, then you better make those moments count. Not being subbed in as much undercuts the message of confidence and trust from the coach and that in turn can bring more doubt to a player's ability to believe in himself.
Compare Ohio State's trajectory this season so far. It is, ironically, similar to that of the 2014 season. I remember watching their loss to Virginia Tech at the beginning of that season, and I concluded that tOSU was not going to be very competitive that year. That loss, however, apparently brought them the right kind of humility to work on improving, playing hard in every game, and they ended up trashing Oregon with a third-string quarterback (after trashing Alabama in the semi-final). Ohio State this season, perhaps having a bad day back in that 2nd game, perhaps being complacent or over-confident, received a helpful shock from that loss to Oregon, and they seem to have something to prove to everyone now.
Maybe to some I am being Captain Obvious, but I think that coaching to handle the pressure of success is a critical element to making it all the way to the top. The teams that succeed at consistently performing at the elite level have mastered coaching how to succeed, how to emotionally and mentally process success, and how to prepare to succeed week after week. The coaches don't just talk about it, they live it because it's a matter of their character and personality.