USC is the first team to lose the No. 1 ranking after a victory since Nov. 3, 2002, when top-ranked Miami dropped after beating Rutgers 42-17 and No. 2 Oklahoma moved up after a 27-11 victory over No. 13 Colorado.
LSU, which recovered from its own first-half malaise to beat Tulane 34-9 on Saturday, received 33 first-place votes from the media panel and 1,593 points. USC got 32 first-place votes, 11 fewer than last week, and 1,591 points.
The voting was the closest since the second poll of the 2002 season, when Miami and Oklahoma tied for No. 1 and each received 27 first-place votes.
LSU is No. 1 in the AP poll for the first time since Nov. 2, 1959.
The rest of the rankings released Sunday bore little resemblance to any of the previous polls, thanks to a crazy weekend in which three of the top five and seven of the top 13 teams lost.
Overall, nine ranked teams went down, seven to unranked opponents.
California moved up three spots to No. 3, Ohio State jumped four places to No. 4 and Wisconsin moved up five spots to No. 5.
The rest of the top 10 featured some unfamiliar names.
South Florida, which knocked off No. 5 West Virginia 21-13 on Thursday night, made it into the poll for the first time two weeks ago. Now the Bulls are No. 6 in the country and West Virginia dropped eight spots to 13th.
No. 7 Boston College is in the top 10 for the first time since 1992. No. 8 Kentucky has a top-10 ranking for the first time since 1977.
No. 9 Florida, which lost 20-17 on a last-second field goal to Auburn, fell five spots. Oklahoma, which lost to Colorado on a field goal as time expired, dropped seven spots to No. 10.
In the USA Today coaches' poll, USC held on to No. 1, with LSU, Cal, Ohio State and Wisconsin in the top five.
The other two top-10 teams to lose this weekend took the largest tumbles in the new rankings.
Texas dropped 12 spots to No. 19 after it was handed its worst home loss of the Mack Brown era, 41-21 at home to Kansas State. The Wildcats entered the rankings for the first time since 2004 at No. 24.
Rutgers fell 11 spots to No. 21 after losing 34-24 at home to Maryland.
The second 10 starts with South Carolina at No. 11 and Georgia at No. 12.
After West Virginia is Oregon at No. 14. The Ducks fell three spots after a tough 31-24 loss to Cal. Virginia Tech is No. 15, followed by Hawaii, Missouri and Arizona State at No. 18.
Cincinnati moved up four spots to No. 20, a week after receiving its first national ranking in 31 years.
Clemson, another upset victim, fell nine spots to No. 22 after losing 13-3 to Georgia Tech.
No. 23 Purdue was the second newcomer to the rankings, along with Kansas State, and No. 25 Nebraska was the only team in the Top 25 to hold the same spot as it did last week.
Falling out of the rankings were Penn State and Alabama.