No. 2 Alabama (12-1) needed a knockout last night at the Superdome in New Orleans. A close decision over No. 1 LSU (13-1) may not have swayed enough voters to win the national championship.

But coach Nick Saban’s defense gave the Tide their knockout, a convincing 21-0 victory in the rematch that left no doubt about which college football team was the best in the nation, at least for one night.

Five field goals gave Alabama a 15-0 lead in the fourth quarter before Trent Richardson broke off a 34-yard scoring run with 4:36 left to play. LSU did not even cross midfield until there was 8 minutes remaining in the game.

I’m not sure the Tigers could have scored 15 points last night even if you gave them another four quarters to play. Alabama was that strong.

Many observers argued that the Tigers had already beaten the Tide in Alabama during the regular season, a 9-6 overtime victory on Nov. 5.  Bring them another opponent, they said. But Alabama’s suffocating defense, with all these weeks to prepare, was more than enough opponent last night. It may not have been fair to LSU, but it was reality.

After the game Alabama received 55 of the 56 first-place votes in the final Associated Press poll. LSU, even after the loss, got the other vote.

Imagine if Alabama had won the game on a field goal at the end of regulation or in overtime. That may have led to a controversy the BCS could not have survived.