AUBURN, Ala. — So many of LSU’s games against Auburn have been tight, heart-pounding classics.

This one was a stinker.

No. 5 Auburn steamrolled No. 15 LSU 41-7 on Saturday night in Jordan-Hare Stadium, ruining the debut start of LSU’s true freshman quarterback and gashing what appeared to be an unfixable defense.

Gus Malzahn’s high-flying, up-tempo offense poured on nearly 400 yards — in the first two quarters — and Auburn soared to a 31-7 halftime lead in a crushing victory in front of a rowdy sellout crowd of 87,451.

LSU (4-2) suffered its worst loss in 15 years — dating to another 41-7 defeat to Auburn in 1999 — and is off to its first 0-2 start in Southeastern Conference play since 2001. LSU managed just 280 yards of offense, and Auburn became just the third team in LSU coach Les Miles’ 10 years to score at least 41 points against the Tigers in a regulation game.

“The film will be the answer,” Miles said afterward. “Coaches will correct it.”

Brandon Harris, a true freshman making his first start, looked nothing like that snazzy quarterback who led the Tigers to impressive drives late in the loss to Mississippi State and in the win over New Mexico State last week.

He misfired a half-dozen times, fumbled and completed just 3 of his first 14 pass attempts before being yanked for sophomore Anthony Jennings with about six minutes left in the third quarter — and LSU down 34-7.

Afterward, Harris heavily criticized himself in front of a gaggle of reporters.

“It was awful from the start to the finish. Everything about it was awful,” Harris said. “Our coaching staff does a great job every week preparing us for each opponent. I flat out came out and played terrible. I can’t even put a grade on it. It’s that low.”

LSU’s struggles at quarterback, coupled with a bevy of defensive woes, are frightening issues for a young, inexperienced team that now must hit the road for a game at Florida (3-1, 2-1).

The reigning SEC champion, Auburn (5-0, 2-0) finished with 566 yards of offense, a 7.6-yard average, and managed to expose what many thought was LSU’s strength: the secondary.

Quarterback Nick Marshall passed for nearly 200 yards in the first half, and Auburn ripped off plays of 18, 19, 56, 19, 38, 26 and 34 yards in the first two quarters, becoming the second SEC team to bury LSU in the first half.

Mississippi State had 263 yards and led 17-3 at halftime in a win at LSU on Sept. 20.

In all, defensive coordinator John Chavis’ group has allowed 642 yards and 48 points in two halves against SEC teams this season, a stunning outcome for a normally stiff defensive crew.

Linebacker Kendell Beckwith said LSU and Mississippi State’s offenses were similar.

“Just coverage breakdowns and missed tackles,” Beckwith said, pointing to the faults Saturday. “Got to limit the big plays and get back to the drawing board. We did a better job of communicating tonight, just giving up the big plays. Just can’t happen.”

Malzahn and his speedy gang put up more points in a first half (31) than any team in Miles’ 10 years. By midway through the third quarter, Auburn had a whopping 14 plays for 10 yards or more, and some fans headed for the exits on a cool night on the Plains.

This rivalry has included some classics known by just a few words: “The Earthquake Game,” “The Night The Barn Burned,” “The Bring Back The Magic Game.”

This won’t make the list, as far as LSU is concerned.

Auburn snapped a three-game losing skid to LSU, and it won for just the second time in seven years against Miles’ crew.

This was tied for the biggest Auburn shellacking in the series, equaling that 41-7 win over LSU in 1999 — known as “The Cigar Game.” It’s a spanking that might have LSU out of the Top 25 for the first time in 87 weeks.

On a week when a host of top-10 teams fell — Oregon, Oklahoma, Alabama and Texas A&M — Auburn smothered LSU from the start.

Malzahn’s Tigers ran for 298 yards and threw for 268. Auburn offensive players slipped out of more than a dozen tackles, and Auburn coasted through the second half after a dominant first half.

A 52-yard pass from Harris to Malachi Dupre set up LSU’s only score late in the first quarter. Harris completed just two other passes for a combined 6 yards.

“We got off to a slow start,” Dupre said. “(Told Harris) to keep his head up, get back to work Monday and get those things corrected like I know he will.”

Auburn had 379 yards in the first two quarters, the most in a half under Malzahn. That includes 18 games and matchups this season against Louisiana Tech and San Jose State.

Auburn rolled up 220 passing yards and 159 yards on the ground.

“We came out and thought we had a good week last week, thought we had a great week of preparation,” LSU defensive tackle Christian LaCouture said. “We’re just going to have to go back and watch the film and see where we messed up and correct it and go to Florida and get a ‘W.’ ”

Malzahn’s offense scored on its first four drives — three touchdowns and a field goal — by burning LSU up the middle and on the outside.

LSU entered Auburn territory twice in eight first-half drives, and Miles had a clock management miscue just before halftime. He failed to use a timeout with LSU at the Auburn 25-yard line. Harris’ pass fell incomplete in the end zone as the first-half clock expired.

It was just one gaffe in a night full of them.

“I’m really shocked,” Harris said. “I feel like we had a great game plan.”