BALTIMORE — The single voice of a Browns fan barking in the lower concourse of M&T Bank Stadium could be heard moments after the Ravens’ 33-30 overtime loss to Cleveland on Sunday.

It was a sound that may have signaled the official end of an era we’ve enjoyed for more than 15 years. Of course, the fall of the Ravens defense didn’t happen overnight as we’ve watched future Hall of Famers ride off into the sunset and other perennial Pro Bowl selections depart, but a unit in transition had still possessed enough talent and swagger to find ways to be more good than bad over the last couple years. Sunday’s performance eliminated any lingering optimism about a defense that had already played poorly at Oakland in Week 2 and was torched by Andy Dalton and Cincinnati in the home opener two weeks ago.

Nevermore.

If giving up 33 points, 505 yards of offense, and 457 passing yards to Josh McCown and the Cleveland Browns — yes, the AFC North doormats that hadn’t won in Baltimore since the George W. Bush administration — isn’t rock bottom, I don’t know what it is. Allowing Tom Brady or Aaron Rodgers or even Philip Rivers to post those kinds of numbers is one thing, but a 36-year-old journeyman shredding you in your own stadium?

Baltimore may still field a defense, but it’s no longer a group worthy of being called a “Ravens” defense.

“I put this on the defense as a whole. We didn’t come through [Sunday],” cornerback Jimmy Smith said. “We were supposed to show up, and we did not show up in the second half.”

Of course, it’d be unfair to rip the defense without acknowledging how ravaged the group was by injuries by the time the Ravens entered overtime on Sunday afternoon. Already without Terrell Suggs and Chris Canty long before Sunday’s game, the Ravens lost their only reliable pass rusher (Elvis Dumervil) and their No. 2 and No. 3 cornerbacks (Lardarius Webb and Will Davis) in the first half, injuries that caused the defense to completely unravel after a respectable “bend, but don’t break” performance over the first 30 minutes.

In overtime, another injury to No. 4 cornerback Kyle Arrington led to rookie Tray Walker playing in the base defense after he’d been a healthy inactive in Pittsburgh last week. A reflection of how little confidence they had in Walker, the Ravens used second-year safety Terrence Brooks at the nickel spot earlier in the game before having no choice but to go to the 2015 fourth-round pick in crunch time.

With the modern reality of the salary cap and other circumstances contributing to where the Ravens currently stand, they knew all along they could only take so many injuries after the offseason departures of Haloti Ngata and Pernell McPhee. Deep depth is a rarity in the NFL these days, and the Ravens are learning that painful lesson in the midst of the worst start in the 20-year history of the franchise.

“Whoever is out there has to play well. Whoever is out there has to get the job done,” head coach John Harbaugh said. “That’s what has to happen. That goes for all of us. As coaches, we have to find a way to put whoever is out there in a kind of position where they can be successful. That all goes hand-in-hand. And that was a very winnable game. We should have won.”

The phrase “next man up” has been a rallying cry in Baltimore for years, but the words have never rung more hollow. The Ravens simply aren’t talented enough with an array of issues on both sides of the ball that are haunting them in some form every week. Blame defensive coordinator Dean Pees as much as you’d like — he needs to own a mess that could ultimately cost him his job — but a defense can only survive so much attrition, whether by injuries or free-agent departures or underwhelming draft picks.

In truth, an offense consisting of receivers and tight ends who required a program to identify scoring 30 points on Sunday should have been more than enough with even an average defensive performance against the Browns, who entered Sunday’s game ranked 20th in the NFL in total offense and points scored.

The defense can’t solely blame the injuries for its demise as the Ravens racked up penalties at crucial times — veteran Jason Babin committed infractions on two different Browns’ touchdown drives in the second half — and key performers such as linebackers Daryl Smith and C.J. Mosley and safety Will Hill also played poorly. If the defense can’t even tackle or count on its known commodities to make plays, what chance does the group really have?

They may be wearing purple and black, but you certainly don’t recognize a defense allowing 27.4 points per game, just a hair better than the franchise-worst 27.6 per contest allowed in the inaugural 1996 campaign. In five games, Baltimore has already allowed 137 points, just 28 fewer than the record-setting 2000 defense surrendered in an entire regular season.

Late in the game on Sunday, which figure in the defensive huddle could players turn to for an emotional lift? Forget having a Ray Lewis or Ed Reed or Suggs; the Ravens didn’t even have a player like Dumervil to make everyone believe they could force a stop.

The Baltimore defense was a ship without a captain in the second half. And it sank hard.

“We’re disappointed, because we know what kind of team we are,” said Mosley, who struggled mightily in pass coverage throughout the game. “We know how [hard] we work, and we’re definitely better than 1-4. We’ve just got to put our foot down and prove that. We play hard, but we’ve just got to finish as a team.”

The Ravens keep talking about their need to finish games and to get off the field on third down — Cleveland went 12-for-19 in that department on Sunday — but they appear more “finished” than able to finish in 2015 with Thanksgiving still more than a month away.

They’re beaten up and bad with no relief in sight as back-to-back West Coast trips loom. Nothing is a given moving forward when you lose to the Browns at home for the first time since 2007 and only the fourth time ever in Baltimore.

Instead of fans celebrating a win with a chance to improve to .500 next week to reboot the season, all that could be heard at the end of Sunday’s game was a single Browns fan barking in the concourse.

And the “Ravens” defense was nowhere to be found.