Let’s not go crowning repeat Super Bowl champs just yet. The Falcons knocked the Broncos from the ranks of the unbeaten Sunday, and in the process made Denver’s elite defense look beatable for the first time in, well, a very long time. As running back Tevin Coleman made big play after big play, racking up 132 receiving yards against Denver’s outmatched inside linebacker corps, the game served as a reminder that the 2015 Broncos’ winning equation was the exception, and not the rule, for how championship teams are built.

Most Super Bowl–winning teams rely on some semblance of balance. Denver was so ridiculously, unbelievably, cosmically elite on defense last year that it literally did not matter how atrociously its offense played. Wade Phillips’s boys rode the combination of a deadly pass rush, a group of speedy sideline-to-sideline coverage linebackers, and three shutdown-caliber cornerbacks to playoff wins over the Steelers, Patriots, and then the Panthers in the Super Bowl. With a quick 4–0 start this year and some random dude we’d never heard of named Trevor Siemian under center, no one would have blamed you if you thought that Denver had simply picked up where it left off last year.

Except this year’s Broncos club is playing with a different calculus: an offseason of teams raiding their cupboard in free agency means they don’t have the depth at every level of their defense that will allow them to completely dominate every game. The margin for error is just too small now, and that means that Denver can’t just win with its defense anymore; it is going to need to get more from its offense. Now, the really bad news.

With a midtier offense to complement its still very good defense, Denver has looked pretty damn unbeatable. Until this week. The offense under Siemian has been significantly better than what last year’s group, under Peyton Manning and Brock Osweiler, produced: Entering Sunday’s game against Atlanta, Football Outsiders had the Denver offense (which ranked 30th at this time last year) at ninth in offensive DVOA — with the 10th-ranked passing attack and the 19th-ranked ground game. Denver came into the game fourth in points per game (27.8) and right near the middle of the pack in many other important offensive categories, including yards per play (5.5, 16th), completion percentage (65.6, 13th), passing touchdowns (seven, tied for eighth), rush yards (423, 13th), and rushing touchdowns (four, tied for eighth).

Siemian isn’t a top-tier thrower, but he’s been a revelation for the Broncos’ offense. He’s completed 67 percent of his passes for 824 yards and thrown six touchdowns to just three picks, and his 8.16 yards per attempt (fourth in the NFL among passers with 50 attempts) is indicative of his efficiency throwing the ball downfield. The offense we saw on Sunday missed this element. Siemian suffered a shoulder injury in the second quarter of last week’s win over the Buccaneers, so first-round pick Paxton Lynch got the start. If there was any thought that Siemian was going to get Wally Pipp’d by the Broncos’ rookie signal-caller, we can put that to bed now. Lynch struggled, held onto the ball too long in the pocket, and was inaccurate downfield all game long. He finished with 223 yards passing, threw an interception, and padded things with a garbage time touchdown against a Falcons defense that came into the game 31st in defensive DVOA.

Lynch didn’t get much help from his teammates, either. With Donald Stephenson on the sidelines with a calf injury, Ty Sambrailo got the start at right tackle, and he surrendered three sacks (which led to two forced fumbles) to Falcons pass rusher Vic Beasley before getting benched. His replacement, Michael Schofield, didn’t fare a whole lot better, giving up a half-sack of his own. In all, Lynch was sacked six times (the Falcons came into the game with just four on the year), and neither Lynch nor Denver’s run game did little to help alleviate the pressure. The Broncos finished with just 84 yards on 24 carries and were forced to all but abandon the rush when they fell behind 20–3 in the third quarter.

In the end, Denver’s offense isn’t built — and isn’t good enough — to engineer a comeback after its defense failed to match up with Atlanta’s excellent scheming. Not with an inexperienced Lynch manning it, anyway. Falcons offensive coordinator Kyle Shanahan and quarterback Matt Ryan consistently attacked the middle of Denver’s defense, putting dual-threat running back Coleman in the slot and having him run routes against linebackers Brandon Marshall and Todd Davis. Two of those catches led directly to Falcons touchdowns. Coleman’s first haul, in the first quarter, set up a Devonta Freeman score.

On the second, which came in the third quarter, Coleman took it in himself as Atlanta capitalized on a Lynch turnover. That touchdown essentially sealed the deal for the Falcons.

Atlanta mapped out a blueprint for how to beat the Broncos — assuming you have an offense built similarly to a Falcons unit that has looked like the best offense in football. You’d better have enough receivers to draw the attention of Chris Harris, Aqib Talib, and Bradley Roby in coverage while simultaneously attacking with two versatile backs like Freeman and Coleman, which you can use to run the ball or create mismatches with the Broncos’ linebackers with equal aplomb. That kind of combination is rare, so despite the loss, it’s far from time to panic about Denver’s defense. The pass rush remains elite, and the Broncos still have those three corners. But through five games, the losses of linebacker Danny Trevathan (who signed with the Bears) and defensive lineman Malik Jackson (who suits up for Jacksonville now) weigh heavily: The linebackers haven’t been as good in coverage, the defensive line has struggled to defend the run, and, as a group, there isn’t as much depth across the board.

Fixing an offense that struggled so badly against the Falcons will be a multipronged approach. The health of a few key players has clearly been a big issue, so getting Siemian — who was “pretty close” to playing Sunday — and Stephenson back from their injuries will make a major difference, but with Denver playing on a short week (the Broncos head to San Diego on Thursday), their availability will remain a question mark.

If Lynch gets another start, whoever lines up at right tackle is going to need some help, so chipping with a running back or tight end on pass plays could alleviate some of the pressure off the edge that so badly affected the rookie thrower. The most obvious way to slow an aggressive rush is to run the ball effectively, so Denver needs to get more from its ground game. After rushing for 282 yards in the first two weeks, that group has gained just 225 yards, failing to crack the century mark in the three games since. But if that fails, using Lynch’s mobility as an asset could provide some relief — the 6-foot-7 signal-caller runs well and was a dual-threat quarterback at Memphis, so incorporating more bootleg throws on play-action fakes, designed keepers on the boot, moving pockets, or even a few designed runs in read-option looks would help keep edge rushers honest. But even with some creative scheming, Denver’s offense has a challenge in front of it, with the Chargers and Texans next up on the slate. Joey Bosa looks like the real deal for San Diego (two sacks in his pro debut), and while Houston looks like a mess on offense, its front seven can bring the heat.

The Broncos had a once-in-a-generation defense last year, but a few key personnel losses have already created some vulnerabilities. This year’s group still gives Denver a chance to win every week. But Paxton Lynch doesn’t seem ready to capitalize. And until he does, Denver will have to sit and pray for that heretofore anonymous man named Trevor.