Auburn fired defensive coordinator Ellis Johnson a day after giving up 55 points to rival Alabama.
Tigers coach Gus Malzahn announced the firing Sunday following a late-season slide that ended with a 55-44 loss in the Iron Bowl.
The Tigers gave up 539 yards to the top-ranked Crimson Tide on Saturday night in the highest-scoring Iron Bowl. They allowed an average of 483 yards and 39 points over their last six SEC games, losing four of them.
Auburn's defense made several key stands in close games en route to the BCS championship game last season.
Johnson spent one season as head coach at Southern Miss after stints running the defenses at Clemson, Alabama, Mississippi State and South Carolina during a four-decade coaching career.