ATLANTA —  For most of this season — and at times Sunday at the Georgia Dome — the story of the Bears’ season has been easy to summarize: The defense has performed well enough. The offense hasn’t.

But that changed Sunday, at least enough for the Bears to leave Atlanta with a crucial 27-13 win over the Falcons that brought their record back to .500.

Had you known that the Bears’ defense would have entered Week 6 as the 17th-ranked unit in the league, you would have thought the Bears were on their way to the Super Bowl. After all, all Marc Trestman’s offense needed was an average defense, right?

But the offense hasn’t been good enough this season, especially in the second half, where they had scored exactly zero touchdowns in their last two games. Sunday’s game appeared to be headed down a similar track, especially when the Falcons scored 10 straight points in the third quarter to tie the game at 13.

But that’s when Jay Cutler unleashed what could end up being a season-changing 74-yard bomb to Alshon Jeffery — a play the offense desperately needed after stalling in the red zone twice in the first half and going three-and-out on their first series of the third quarter.

“I mean, kind of,” Jeffery said when asked if he was surprised he was so wide open.

He shouldn’t have been surprised. The problem with the Falcons’ secondary this year is that, well, sometimes they just don’t play defense. And that’s all the more reason for an underachieving Bears offense to be severely frustrated with only 13 points at that juncture in the game.

Of course, the pass to Jeffery only got the Bears down to the 6-yard-line, which probably had many wondering if the offense would be held to a field goal once again. But the situation provided the perfect moment for Matt Forte’s first rushing touchdown of the season — an unfair statistic for the guy who has been the Bears’ best offensive player this season.

So why not get him two? That’s what the Bears did after the defense forced a three-and-out and put the ball back in Cutler’s hands for a 15-play, 87-yard drive that burned 8:28 off the clock. Staring at 3rd-and-goal from the 9-yard-line, it looked like another drive was going to stall short of the goal line, but that was before Trestman called a gutsy inside-run that sprung Forte into the end zone for the second time.

“Before the snap, I saw that they kind of backed off in coverage because they thought we were passing the ball,” Forte said. “It was a quick, hidden play. The offensive line did a great job of securing the front guys, and they kind of just ran the other guys in the end zone.”

It was one of those plays that would have had fans questioning Trestman all week if it didn’t work. Instead, it turned out to be the play that finally allowed the offense to say: “We did enough to win.”

But to their credit, that wasn’t the message in a locker room that wasn’t as upbeat as you might think.

“We gotta get better,” wide receiver Brandon Marshall, who caught six passes for 113 yards, said. “That wasn’t good enough. We gotta get better.”

Given how bad the Falcons’ defense is, he’s right. But Sunday the offensive performance was enough, especially with Cutler making smart decisions and avoiding “the big one” en route to 381 passing yards.

Meanwhile, the defense did more than enough. With their top four linebackers all missing the game, a patchwork group consisting of Darryl Sharpton, Khaseem Greene and Christian Jones not only avoided mistakes, but actually played pretty well.

“These guys did great,” Trestman said after the game. “It starts with (defensive coordinator Mel Tucker) and our staff with (linebackers coach) Reggie Herring getting those guys ready.”

Herring especially deserves the credit as he’s a big reason why Sharpton was signed off the street Sept. 25. Herring coached Sharpton in Houston, including last year when the linebacker made the defensive calls for the Texans and led the team in tackles. So when the Bears needed an extra linebacker in late September, Chicago became a natural fit for Sharpton, who had been rehabbing an injured ankle back in Washington D.C.

And there Sharpton was, just a little over two weeks later, starting at middle linebacker for the Bears and relaying the defensive calls to the rest of his teammates.

“It made the transition a lot easier, having someone that I’m very familiar with,” Sharpton said. “(Herring) coached me for three years so that was a huge help. I have to thank him tremendously for getting me prepared.”

Sharpton wasn’t just prepared, he was pretty good. Showing off speed the Bears haven’t seen much at linebacker this season, he connected on the kind of hits that made the Falcons think twice about coming over the middle.

When’s the last time the Bears have been able to say that?

Greene, meanwhile, led the team with eight tackles and Christian Jones provided an edge rush on blitzes.

Of course, the young linebackers were helped tremendously by a defensive line that finished the game with four sacks. With Jeremiah Ratliff back from a concussion, the middle of the line collapsed the pocket and the defensive ends brought Matt Ryan to the ground. With two more sacks Sunday, Willie Young now has seven on the season, while Jared Allen recorded his first as a Bear.

“You can talk about me and Jared getting there, but when you have the two inside guys pushing the pocket in the middle and a quarterback like (Matt) Ryan that wants to step up directly in the pocket, it’s night and day,” Young said.

It was also night and day compared to how the Bears’ defense performed last year when injuries decimated the unit, including at linebacker. But that’s why general manager Phil Emery went out and spent the money he did on the defensive line.

So far the result on defense has been a unit that has been good enough to win.

And for the first time in a few weeks, the offense could say the same.

Adam Hoge covers the Bears for 87.7 The Game and TheGameChicago.com. Follow him on Twitter at @AdamHoge.