A candid and resolute Sean Desai acknowledged Friday that the Bears defense has not performed up to its own standards in recent weeks.

But the first-year defensive coordinator expressed confidence that the unit will revert to the form it displayed earlier in the season, particularly in wins over the Bengals and Raiders, two of the AFC's top teams.

The defense struggled last Sunday in a 33-22 loss to the 49ers, failing to force a punt or a turnover or record a sack or even a quarterback hit.

The Bears permitted plays of at least 21 yards on seven of San Francisco's eight possessions before the 49ers ran out the final 1:12 with three kneel-downs. That included Jimmy Garoppolo pass completions of 83 and 50 yards to Deebo Samuel and Elijah Mitchell runs of 39, 27 and 27 yards.

"Too many explosive plays," Desai said. "That's not who we want to be, and we want to tackle better. Those are the two big takeaways."

After permitting only nine points on three field goals in the first half, the Bears allowed touchdowns on the 49ers' first three possessions of the second half, enabling San Francisco to turn a 16-9 deficit into a 30-22 lead.

"It wasn't a good day, and I would take it a step further: really, we played 11 minutes of bad football in the second half," Desai said.

"That starts with me and it's going to end with me. The players know where they're accountable and where they can execute better. I know where I'm accountable and I can execute better, and the staff does as well. We will be better than that. That's our worst 11 minutes of football that we've played this year."

The game's momentum swung midway through the third quarter. On third-and-19 from the San Francisco 16, Samuel caught a screen pass and raced 83 yards to the Bears' 1, setting up a key touchdown.

"You can always, after the game, look at the calls that you make," Desai said. "I do it every game, every single call that we make in the game. You can always say based on the play that came out, 'I should have done this, and I did that.' And then the other part is we've got to get off blocks and make plays and run to the ball. You can't go back door on blocks, and when you get a one-on-one opportunity versus a blocker, we've got to be able to shed and disengage and get the guy down."

Another play that Desai dissected was Mitchell's 5-yard TD run early in the fourth quarter. The 49ers running back was initially stopped, but his teammates helped push him the final four yards across the goal line.

"That's gut-wrenching," Desai said. "You don't want that because that's a stopped run. It should have been a 1-yard gain. It's a stalemate and their second effort was better than ours, and that's not what you want put on tape, and that's not been characteristic of us. I want to make sure that's clear. That's not been characteristic of this defense."

Desai understands that "you are what you most recently put on tape," but he also knows that the defense can completely flip the narrative Monday night when the Bears visit the Steelers in Pittsburgh.

"I think everybody in our organization for sure and our players for sure know what our standard is," Desai said. "When you don't uphold that standard, it hurts, and it should hurt because it means something to you.

"Now, the great thing is we've got another chance. We've got another opportunity to rectify against another team here that plays to their standards, and they've held their standards for a long time and the type of brand of football that the Pittsburgh Steelers play. So, it's going to be a great opportunity for us to kind of shake that one off."

Desai is convinced that the Bears defense will, with apologies to Taylor Swift, shake it off.

"I'm always very confident and you've got to be," he said. "I believe in our guys. I believe in our coaching staff. I believe in myself. We're going to stay the course. This is not a panic-type of situation. Like I said, we play good football and we played 11 minutes of bad football, so we've got to fix those 11 minutes and make sure that's not what persists the rest of the season and get back to kind of what we know and what our identity is and uphold that."