Alexander rushed for 3,565 yards in his four seasons with the Tide, while Henry needed only three seasons to break the record.
The record-breaking run was a two-yard gain in the third quarter on second and 17.
Alexander was in the building to see his record fall.
Henry, the 2015 Heisman Trophy winner, entered the game with 2,061 rushing yards and 25 touchdowns, both school and conference single-season records. His touchdown run in the first quarter gave him 20 consecutive games with a score.
- Dan Gartland