Falling out after losses were Washington, Georgia Tech, Illinois and defending national champion Auburn.
Nos. 13-18 were Nebraska, South Carolina, Virginia Tech, Michigan and Houston, which has its best ranking since 2009.
Joining the four teams moving into the rankings at the bottom were No. 22 Georgia, No. 23 Arizona State and No. 25 West Virginia.
For Alabama and LSU, the No. 1 vs. No. 2 matchup likely will decide which of the SEC West rivals plays in the conference championship and could ultimately determine which teams plays for the national title in New Orleans on Jan. 9.
LSU's only appearance in a 1-2 game was in the BCS title game in 2008. This will be Alabama's sixth No. 1 vs. No. 2 game, but first in the regular season.
The last time there was a No. 1 vs. No. 2 matchup in college football not played in a bowl or conference title game was 2006, when No. 1 Ohio State beat No. 2 Michigan on the final weekend of the Big Ten's regular season and went on to lose the BCS championship game to Florida. Earlier that season, top-ranked Ohio State also played No. 2 Texas.