The Tigers, 10ï¾½-point underdogs, led 17-0 at halftime and used a stifling defense to shut down the SEC's top offense.
Auburn (8-4, 5-3 SEC) was playing its fourth-string tailback in his first start and went without a fullback in an injury-depleted backfield against the nation's top-rated defense.
The Crimson Tide (9-3, 6-2) had won five straight games but couldn't score on three fourth-quarter trips across midfield.
After the game, Auburn players took turns brandishing the school's banner in front of their fans before finally heading to the locker room. Many of the players returned a few minutes later.
The visitors won for the fourth straight year in the Iron Bowl; Auburn was hammered 31-7 last year. Alabama did halt its century-old scoreless streak against Auburn in Tuscaloosa, but the Tide has been outscored 91-7 on its campus in the rivalry.
Campbell finished 10-of-18 for 169 yards with an interception.
Smith, who carried 25 times, was only called into action with injuries to Carnell Williams (broken leg), Ronnie Brown (sprained ankle) and Chris Butler (pulled groin).
Alabama turned it over on downs three times in the fourth quarter.
The Tide took it to Auburn's 36-yard line with about five minutes left on Dre Fulgham's 40-yard catch-and-run. Then, Mark Brown sacked backup quarterback Brodie Croyle, and Croyle threw two straight incompletions before Carlos Rogers made the Tigers' 20th interception of the season with 3:15 to play.
Alabama drove to Auburn's 35 at the end of the game but came up short again.
The Tigers had blown a 14-3 halftime lead in a loss to No. 6 Georgia last week, when the offense couldn't get a first down and the defense gave up a late touchdown pass.
The nation's top-rated defense set up Alabama's only points, with Waine Bacon intercepting a deflected pass on the Tigers' second offensive play after halftime.
Santonio Beard capped the 46-yard drive with a 1-yard touchdown run with 6:40 left in the third. Alabama's offense, which has scored on 17 straight trips inside the opponent's 20-yard line, wouldn't make it that far again.
Campbell threw for 141 yards and Smith ran for 99 before halftime against a defense that came in giving up 244 yards per game.
The Tigers only gained 78 yards after halftime, but it was enough.
Campbell hit Johnson for touchdown passes of 14 and 11 yards in the first quarter, capping the first two drives. The first was set up by Smith's 51-yard run up the gut, and the second by Roderick Hood's 36-yard punt return to midfield.
On the second touchdown, Johnson was wide open in the middle of the end zone after Alabama came with the all-out blitz.
The Tigers added Damon Duval's 40-yard field goal in the second quarter.
Alabama, meanwhile, turned it over on downs twice in the half. Its offensive staples -- the draw and option plays -- were mostly ineffective throughout the game.