The last two matchups between USC and Notre Dame haven’t exactly been close. The Trojans won 38-3 in 2008 and 38-0 in 2007.

And this time, No. 6 USC (4-1) is coming off of a dominating 30-3 win over Cal, and No. 25 Notre Dame (4-1) has won its last three games by a combined 13 points.

So why are the Trojans not the overwhelming favorite to beat the Fighting Irish on what is expected to be a frigid Saturday afternoon in South Bend, Ind.?

Damian Williams (18) celebrates with Jeff Byers (53) and Kristofer O’Dowd (61) after a touchdown against Notre Dame in 2008.

“If you look at rankings, that’s where you get beat,” redshirt junior receiver Damian Williams said. “We beat a ranked team and then lost to an unranked team. The ranking doesn’t mean much, but this is a big rivalry for us.”

The rivalry between USC and Notre Dame is indeed a storied one. Saturday will mark the 83rd time the teams have met, with Notre Dame the victor in 42 games.

USC has won the last seven battles — dating back to the second year of coach Pete Carroll’s tenure.

But there’s no clear path to victory for the Trojans. They’ve had their own bumps in the road in 2009.

The Trojans have beat Ohio State and Cal on the road, but they have also lost to a Washington team fresh off of a 15-game losing streak and failed to cover the spread against a pitiful Washington State team.

It’s safe to say that both teams are essentially in a must-win situation.

For USC, it’s a chance to rack up another top-25 road victory. A loss would mean elimination from national championship contention.

For Notre Dame?

“USC is one of the best teams in the country,” Notre Dame coach Charlie Weis said. “They’ve beaten us seven times in a row — that’s really the bottom line. Some of them have been ugly. So I think winning this week would do wonders for the spirits of everyone affiliated with Notre Dame.”

The Trojans will have the services of three key players returning from injuries.

Junior wide receiver Ronald Johnson is expected to make his season debut after breaking his collarbone in the fall mock game. Sophomore defensive lineman Armond Armstead broke his left foot in a practice accident and has been practicing with the team since last week. Redshirt freshman cornerback Brian Baucham has missed the last three games after a motorcycle accident last month, but he’s making the trip to South Bend.

The plan is for all three to split time in the rotations at their respective positions.

As for the Fighting Irish, they bring a talented offense to the table.

Junior quarterback Jimmy Clausen leads the nation in passing efficiency. Junior wide receiver Golden Tate, who Carroll likened to “a running back at receiver,” has proven a true dual threat while lining up at both spots. Junior tailback Armando Allen Jr. has put up two 100-yard games already.

“They’re a team that’s interesting,” Carroll said. “They’re willing to throw the ball a bunch if they think that’s what’s necessary in the game plan. Sometimes they’ll go the other way. They’re not a set style that you can tell what they’re going to do in a game plan.”

Save for its season opener, though, every Notre Dame contest has had a set style: They haven’t been decided until the finish.

First, Michigan’s freshman quarterback Tate Forcier threw the game-winning score with 11 seconds remaining to shock the Irish. Then, a touchdown pass from Clausen to tight end Kyle Rudolph with 25 seconds left gave the Irish the victory over Purdue. Tate caught a 33-yard bomb for what would be the game-winner with five minutes left in the Michigan State game. The Washington game didn’t end until overtime.

“They have the confidence of being able to hang in very difficult games and come back and win and all of that,” Carroll said. “All that just adds to your mindset. They’ve got to be just about as strong as they’ve been in years.”

Clausen has been the constant behind most of Notre Dame’s success. He’s completed more than 67.6 percent of his passes this season for 1544 yards and 12 touchdowns — a marked improvement from his freshman year, when he finished the season with just seven touchdown passes and was forced to miss the USC game due to an injury.

“I think they’re a lot better team than they were then,” Williams said. “A lot of the younger guys from the past couple years have developed. I think the experience factor is the reason why they’re a lot better team.”

And the rivalry?

“We have a lot riding on it,” Williams said.