Heading into the 2012 college football season, few could have envisioned this situation.
Yes, many believed that the No. 1 team in the country would be on the field when USC and Notre Dame went head-to-head in what is the regular season finale for both teams; it's just that few could have predicted that it would be the Fighting Irish, and not the Trojans, who would enter the showdown as the nation's top team.
But that's why a national champion isn't crowned during the preseason polls, as USC went from being ranked No. 1 in both the AP and USA Today Polls to finding themselves outside of the Top 25 heading into their final game of the season.
At the other end of the field, Notre Dame has gone from being unranked in the preseason polls to being No. 1 in the latest BCS rankings, and have set themselves up to earn an invitation to the BCS National Championship Game with a win over the Trojans.
Going into Saturday's all-important matchup, here's a look at what the Fighting Irish have to do to preserve their undefeated season.
Pressure on the Quarterback
Heading into the season, USC's biggest weapon was quarterback Matt Barkley, who was considered to be one of the top candidates to take home the 2012 Heisman Trophy.
Though Barkley has had some big games, such as three outings with at least five passing touchdowns, the star signal-caller hasn't quite lived up to expectations. That doesn't matter to Notre Dame, because USC will be without Barkley on Saturday, as the senior has been ruled out due to a shoulder injury.
In his absence, the Trojans will go with Max Wittek, who has thrown all of nine passes this season, and is an obvious downgrade from Barkley, who is among the nation's most dangerous offensive players through the air.
The Irish need their overwhelmingly effective pass rush to be at its best against the Trojans, even without Barkley on the field, because Wittek has elite receivers in Marqise Lee and Robert Woods at his disposal, and both are capable of putting up big numbers against any defense.
Nonetheless, if Manti Te'o and the Fighting Irish play the way they have all season, they'll lead Notre Dame to a win, simply because USC won't be able to put enough points on the board to stay in the game.
More Production on Offense
Since the start of the season, the knock on the Irish has been that their offense isn't on the same level of other elite programs such as Oregon, Kansas State, Alabama or Georgia—but that hasn't mattered, as Notre Dame has continued to win despite a lackluster offense.
On Saturday, though, Brian Kelly's team should be focusing on getting more production out of their offense, because against any of the other national title contenders, it'll be tough to win without the offense making an impact.
Heading into the game, Notre Dame's offense sits 80th in the nation in passing yards and 32nd in rushing yards, so Kelly should be looking to get a better performance out of sophomore quarterback Everett Golson, who registered his first three-touchdown passing game of the season last week against Wake Forest.
Furthermore, if Notre Dame is to beat USC, Golson will have to limit his turnovers as well, because as we saw when the Fighting Irish took on Pittsburgh and Michigan, when he throws picks, the Irish struggle.
If he can generate more offense without turning the ball over, the Irish will roll to their first undefeated season since 1988.