Sunday was not kind to last season's NFL semi-finalists.
Two are 1-3, another was shut out at home for the first time since 1993 by a division rival, and the only unbeaten team of the bunch may have lost its starting quarterback for an unforeseen amount of time.
In the case of the defending Super Bowl champion Denver Broncos, the lone 4-0 team in the NFL, they may be no worse for wear without Trevor Siemian. Rookie Paxton Lynch saw his first regular-season action when Siemian exited Sunday's game with a shoulder injury and did more than enough for the Broncos to cruise in a 27-7 victory over the 1-3 Buccaneers.
Siemian sprained the AC joint in his non-throwing shoulder and coach Gary Kubiak said he probably could have returned, but Denver's bigger worry should be the Atlanta Falcons when their NFL-leading 34.7 points per game roll into Mile High Stadium next week to face the Broncos' vaunted defense.
Just ask the Carolina Panthers how that worked out for them.
Last season's runners-up suffered a 48-33 shellacking in Georgia as their NFC South rival, led by Julio Jones, ran circles the size of Josh Norman's mouth around Luke Kuechly and co. to fall to 1-3 in their Super Bowl hangover. Out of seven previous teams under the modern playoff format to start 1-3 or worse after a title game appearance, only the 1996 Cowboys made the playoffs.
What's worse, Cam Newton suffered a concussion during the loss as the Panthers' offensive line continues to falter around the reigning NFL MVP, who dipped and dodged to just 165 passing yards before exiting in the fourth quarter. He was entered into the league's concussion protocol with his Week 5 status up in the air.
The same can be said about Carson Palmer, who started opposite Newton in last year's NFC championship game and may be just as integral to his team's dwindling playoff outlook.
Indeed, the Arizona Cardinals are a mess and in last place in the NFC West after blowing a 13-10 lead to the Los Angeles Rams after Palmer's exit. The 36-year-old quarterback went end-over-end in the fourth quarter and landed on his head, sending him to concussion protocol, while Drew Stanton squandered the Cardinals' final two drives with a pair of interceptions.
Maybe equally surprising as Arizona's unforeseen struggles is the fact the Rams are 3-1 and tied for first place with the Seattle Seahawks.
Ah, first place, where the New England Patriots have come to thrive for the better part of a decade. But Bill Belichick's crew suffered the most painful of losses on Sunday, a 16-0 beatdown courtesy of Rex Ryan's Buffalo Bills. You'll need to time travel 24 years to find the last time a Belichick-coached team was shut out at home: Sept. 27, 1992, when he was with the Cleveland Browns. Jacoby Brissett, the Patriots' starting quarterback on Sunday, was born three months later.
It was just the second time since 2009 the Patriots have lost to an AFC East team at Gillette Stadium as Buffalo, with just one win in Foxborough since 2002, dictated play wire to wire in a complete role reversal.
Don't feel too bad for them, though. They're still 3-1, improbably, and Tom Brady makes a triumphant return from his Deflategate-cation next week against the Browns.
ANSWERING THE BELL
Pittsburgh Steelers running back Le'Veon Bell returned from his three-game suspension and made his presence felt in his season debut, totalling 178 yards from scrimmage. It opened everything up for his team-mates in the 43-14 win over the Kansas City Chiefs. Quarterback Ben Roethlisberger threw five touchdowns -- two to Antonio Brown -- as he finished 22-of-25 on the night.
There were a number of firsts amid the 571 total yards the Falcons dropped on the Panthers defense. Matt Ryan completed 28 of his 37 passes for a Falcons-record 503 yards and four touchdowns, and Julio Jones had 12 catches for 300 yards, becoming only the sixth player to break the 300-yard mark in a game. The Falcons, already with the NFL's top-scoring offenses entering the week, have scored 45 or more points in back-to-back games for the first time in franchise history.
New York Jets quarterback Ryan Fitzpatrick followed up an historically awful six-interception performance last week with three picks in a 27-17 loss to the Seattle Seahawks. Two of the interceptions came in the fourth quarter, giving Fitzpatrick 11 fourth-quarter picks over his last five games.
Dallas Cowboys rookie quarterback Dak Prescott again went interception-free in a 23-of-32 performance complete with 245 yards and the first two-touchdown game of his young career. His 131 pass attempts without a pick are the most in NFL history to start a career.
Will Fuller had himself a day in the Texans' 27-20 victory over the Titans. The rookie wideout was Houston's leading receiver, with 81 yards and a touchdown on seven grabs, and added a 67-yard punt return for a touchdown that served as the eventual game winner.
Jones and Ryan reached their milestones on this electric 75-yard catch and run by Jones.
Raiders quarterback Derek Carr engineered yet another comeback win, made complete by Michael Crabtree's third touchdown catch of the game with 2:12 to play. Oakland held on for a 28-27 victory over the Baltimore Ravens, giving Carr his sixth game-winning drive since the start of the 2015 season -- the most in the NFL.
THE REAL MCCOY
"That performance in the second half is flat out unacceptable," said an furious Mike McCoy, whose San Diego Chargers blew a 13-point lead in the fourth quarter before losing 35-34 to the New Orleans Saints. "We absolutely gave this one away. Everything falls on me. I'll take the blame for everything that happens. We're going to find out a lot about this football team in a hurry."
After handing Bill Belichick an embarrassing home shutout loss, Rex Ryan did his best impression of his curmudgeonly counterpart.
"On to Los Angeles," a monotone Ryan quipped to reporters as an ode to Belichick's infamous line from a couple of years ago ("On to Cincinnati") after the Pats were shelled by the Chiefs on the road. In his trademark good mood, he then boasted about "my sources inside the New England Patriot building" and said the Bills "expected to win" in the absence of Tom Brady.