Alabama football has had backup quarterbacks deliver in big games before Monday night. Steve Sloan did it in the 1964 Sugar Bowl, subbing for a suspended Joe Namath. Namath missed curfew several days before the game. Every Alabama football assistant but one lobbied Bear Bryant to let Joe play. The one who did not was Gene Stallings. Bryant agreed and Joe remained in Tuscaloosa when the team left for New Orleans.
The Crimson Tide won, beating Ole Miss 12-7 on a frigid Tulane Stadium turf. Tim Davis kicked four field goals for all the Tide points.
Setting aside that bit of history along with other less noteworthy backup QB stories, nothing comes close to Tua Tagovailoa.