OC: Homer Smith vs. UGA in 1994.
I always thought Gene Stallings and Homer Smith could have been an all-time great combination....if Stallings had been constitutionally able to embrace change. Unfortunately, he wasn't, and it limited his success in the last couple of years. The game evolved, but Stallings didn't. In fact, I think he steadfastly refused to acknowledge that change was even warranted.
That characteristic separates really good coaches (Stallings and Les Miles, for example. You could make a good case that Spurrier falls into this category as well.) from truly great coaches (Bryant and Saban).
The great ones manage to keep an underlying philosophy / strategy while updating their tactics, evolving as the game does. The good ones are fantastic at executing their tactics, but can't (or won't) admit even to themselves to that those tactics and attendant skill sets are no longer the best way.
Admittedly, a fine line to walk. But that's what separates the good from the great.
DC: Bill Oliver vs. Miami in 1992.
Oliver's ego got in the way later, largely driven by the acclaim he got for the Miami game, and he kind of fouled his nest on the way out. But you can't say that that one game wasn't a masterpiece for the ages.