BEREA, Ohio – Through the first three quarters of a game, the Cleveland Browns' defense has been among the NFL’s best.

But in the fourth quarter, Cleveland’s defense has been perhaps the very worst.

Defensive fourth-quarter collapses are the biggest reason why the Browns are just 2-2, despite playing one of the league’s easiest schedules to this point.

Now, with five of the top 10 teams in ESPN’s power rankings coming up on the slate before December, Cleveland’s season could approach a breaking point if its late-game issues on defense aren’t fixed -- and fast.

“Obviously, you’re trying to play four quarters of football. ... Unfortunately, we’ve had some issues in the fourth quarter that have led to points,” coach Kevin Stefanski said. “We unfortunately [have given up] up big plays that really can’t happen and shouldn’t happen. I think we’ve gone a long way in working on those type of things. We just have to continue to play sound football, get lined up No. 1, play the defense and execute.”

Cleveland has yet to face a top-18 offense, according to ESPN’s Football Power Index. But in the first, second and third quarters, the Browns defense has still been solid if not stout.

In the first three quarters, opposing offenses are averaging just 4.93 yards per play which is seventh-best in the league.

But in the fourth quarter, the Browns are surrendering a whopping 7.83 yards per play. That ranks last by a considerable margin. No other defense is giving up more than 6.61 yards per play.

The Browns are also giving up more points in the fourth quarter (12.5 points per game) than they are in the first three quarters combined (11.25 points). They are giving up more points in the fourth quarter than any team in the league as well.

Only the Seattle Seahawks (-14.94) and Detroit Lions (-15.46) own a worse defensive EPA (expected points allowed) than the Browns (-13.26).

“Just have to play 60 minutes of football. Have to tighten it up in the fourth quarter,” said safety Grant Delpit. “We’re pretty bad in the fourth quarter right now. That’s not what great teams do.”

Defensive miscues in coverage have been the primary – though not only – culprit.

In Sunday’s loss, Cleveland had the Atlanta Falcons pinned inside their own 10-yard line with 3 minutes left to play and the game tied 20-20.

But off play-action, slot receiver Olamide Zaccheaus found a wide-open hole in Cleveland’s Cover 3 coverage. Drake London cleared out cornerback Denzel Ward and safety John Johnson III with a go route. And with Cleveland’s linebackers not playing deep enough, Zaccheaus was able to generate 9.9 yards of separation, according to NFL Next Gen Stats. A 42-yard completion, combined with a 15-yard face-mask penalty on Ward set up Atlanta’s game-winning field goal.

“That was a long-drawn out play,” Johnson said, “and we just lost a guy.”

Losing track of opposing receivers at inopportune moments hasn’t been the only issue.

Cleveland’s linebackers were attacking the line of scrimmage in Atlanta because the Falcons ran the ball at will in the fourth quarter.

"What happens when you run the ball that many times and you are thinking, 'Run, run, run,' you are thinking the same thing is going to happen, but you have to read your keys and execute your responsibilities. We were not clean on that play, and that's how we got hit," said Browns defensive coordinator Joe Woods.

The Browns gave up 7.5 yards per rush in the fourth quarter in Atlanta. And on its fourth-quarter touchdown drive, the Falcons handed the ball off 10 straight times while marching 75 yards for a score.

The Browns were down three defensive starters along the line in Atlanta, including star pass-rusher Myles Garrett. But the Falcons were without standout running back Cordarrelle Patterson, who sat the second half with a knee injury. A running back committee of Caleb Huntley, Tyler Allgeier and Avery Williams gashed the Browns instead.

“They got theirs, which is going to happen, but it’s always a combination of things,” Stefanski said of the run defense falling apart late. “It’s always one guy here, one guy there. You always question, ‘Could I have put them in a better position on the playcall?’ All of those things. There’s not one answer to that.”

As the Browns search for answers, the degree of difficulty is about to get much tougher.

In their next seven games, the Browns play six of the top 11 ranked offenses, according to FPI, beginning Sunday with the Chargers (1 p.m. ET, CBS), who put up 47 points on Cleveland last season.

A barrage that included 26 points in the fourth quarter alone.

“Each and every play, we have to be locked in, or we’re going to get torched,” Johnson said. “They’ve been doing [it] to everybody, dating back to last year, too. We need our best effort.”