Kevin Steele didn't hesitate to take full responsibility for what he called a "frustrating" and "really unacceptable" performance from Auburn's defense in its 22-21 loss to LSU on Saturday night.

Steele took the brunt of the blame for it, noting that it's his responsibility as defensive coordinator to make sure opposing teams don't walk into Jordan-Hare Stadium and hang 22 points on the scoreboard. Despite that, the third-year defensive coordinator said 90 percent of his defense's snaps against LSU graded out as "really good football" as Auburn held LSU to 8-of-20 on third downs and just 2.9 yards per carry with just a 42.8 percent completion rate on pass plays.

It's the remaining 10 percent of those snaps that made the difference, with some of that coming in the fourth quarter as Auburn's lead dissipated and transformed into another heartbreaking loss to its division rival. There were the two costly pass interference calls on LSU's game-winning drive, but penalties aside, two plays in particular stood out during the fourth quarter: LSU's 71-yard touchdown pass to get within two points midway through the quarter, and the fourth-and-7 conversion late to extend LSU's decisive drive.

So, what went wrong for Auburn's defense on those two plays?

First, let's take a look at the 71-yard touchdown from Joe Burrow to Derrick Dillon with 8:18 to go in the game. Following an Auburn punt on the previous possession, LSU took over at its own 29-yard line. In a three-wide set, Burrow faked a handoff to Nick Brossette and then dropped back with a seven-man protection -- something LSU did often on Saturday --before stepping up in the pocket and finding Dillon across the middle of the field.

Deshaun Davis saw the play develop from his spot at middle linebacker, and when Burrow lofted the pass to Dillon, the Auburn senior linebacker thought he was in perfect position to make a play. Davis leapt at the 45-yard line, hoping to make the interception, but the ball went just past his outstretched fingertips and found Dillon at midfield.

"I thought I did, but I judged the ball wrong, I guess," Davis said.

Dillon caught the ball and quickly turned upfield. Safety Daniel Thomas appeared to be in good position to make a tackle, but the junior was caught flat-footed and couldn't recover as Dillon raced down the right sideline.

Jeremiah Dinson had a chance to bring Dillon down inside the 15-yard line, but his diving attempt at a sideline tackle was unsuccessful, and Dillon cruised into the end zone for the score.

"Just missed tackling," Dinson said. "Just a couple of missed tackles. I should have made the tackle on my own, but like I said, they made plays and did a good job."

It was the longest pass play surrendered by Auburn's defense since Steele took over prior to the 2016 season and just the second pass play of at least 70 yards during his tenure. The other came last season against ULM, when Garrett Smith found Brian Williams for a 70-yard touchdown against Auburn's reserve players late in the fourth quarter last November.

Dillon's touchdown was also just the second-longest play from scrimmage allowed under Steele, behind Texas A&M's Trayveon Williams' 89-yard touchdown in 2016. It was also the second straight season Auburn has allowed a 70-yard play against LSU, as Russell Gage had a 70-yard run in Death Valley during last season's game.

"Somebody just didn't do their job," Steele said. "Pretty routine play. Not a fancy play, pretty routine play. You've seen it in fall camp, in fall practice. Played the coverage against it. We just had a mental error."

Davis tried taking the blame for the play himself, which Dinson said was understandable "because that's Deshaun" and it's how he is as the leader of the defense, but it's hard to fault him for failing to come up with a takeaway on a ball just out of his reach. Instead, Dinson said, the blame is on the defense as a collective unit.

"You can't think that a guy is going to make a play, because you see what happened: The guy caught it and he took it for a touchdown," Dinson said. "We just got to play better."

The other critical letdown came with 2:09 to play and LSU facing fourth-and-7 from the Auburn 48-yard line. LSU went to a four-wide set with one running back lined up next to Burrow in the shotgun. Auburn rushed five on the play, but Burrow was able to get rid of the ball quickly and found Stephen Sullivan on a slant to the right hashmark for a 9-yard gain and a first down before he was tackled by a diving Thomas.

"If you undercut a ball you've got to get it," Steele said. "You can't undercut a ball if you don't get it and so other than that, no, it came out pretty quick and we were in pressure."

Defensive end Marlon Davidson credited the fourth-down conversion to a lack of focus from Auburn's defense.

"Ain't no way another team gets a fourth-down play on us," Davidson said. "They don't convert that. We hold our defense to a different standard. We play hard on third, fourth, first, second down. No matter what, nobody don't get nothing on us. That's the pride of our defense, because we're stupid D, and we let that down today."

The fourth-down conversion extended LSU's drive, and two plays later Jamel Dean was called for pass interference that put LSU in field goal range. It was the second such flag on the drive, the other coming earlier against Dinson on a third-down in LSU territory, and it allowed LSU to run out the clock before Cole Tracy's 41-yard field goal as time expired to hand Auburn its first loss of the season.

"The backbreaker is, in basically a 60-yard drive, we gave up 30 yards in penalties," Steele said. "The last drive, they earned half of what they got. We gave them the other 30 yards. And that's on me. We worked really hard after the Washington game to make sure that we were, we got better, at making sure there was no question, no question about the interference. But obviously we have not made enough progress in that area yet."

Tom Green is an Auburn beat reporter for Alabama Media Group. Follow him on Twitter @Tomas_Verde.