ATLANTA — It was a long way down for the Carolina Panthers on Sunday. Carolina, a team that routinely, some say excessively, prances about the sidelines in celebration, finally felt the sting of a loss after 14 straight wins this season. Losses are not taken easily around the N.F.L., but the Panthers’ locker room was unusually subdued, as if the music were accidentally halted at the height of a party.
The Panthers were sideswiped in their bid to be the first 19-0 N.F.L. team, losing to the Atlanta Falcons, 20-13, before an announced crowd of 70,981 at the Georgia Dome. The Falcons’ defense held the N.F.L.’s top-scoring offense (32.1 points a game) to one touchdown, and quarterback Matt Ryan’s play-action passes, and an acrobatic touchdown reception by wide receiver Julio Jones, ended the Panthers’ run.
No one took the loss harder than Carolina quarterback Cam Newton, who sat alone in front of his locker with his head bowed while his teammates gave postgame interviews. Newton finally walked to a lectern to talk to the news media an hour after the game. He took his share of the blame.
He said that the Panthers had been beaten badly and that to a high degree, “we deserved it.”
Newton added: “I’m talking with the mirror in front of my face. That’s unacceptable, especially this time of the year. We have to be jelling and meshing.”
The Panthers ripped the Falcons, 38-0, just two weeks ago in Charlotte, but Carolina Coach Ron Rivera insisted that his team had not taken Atlanta (8-7) lightly. “Just disappointing,” Rivera said of the loss. “We didn’t play very well.”
Carolina will host Tampa Bay next week as the Panthers try to lock up home-field advantage throughout the N.F.C. playoffs.
The Panthers played without their leading rusher, Jonathan Stewart, who missed his second straight game with a sprained foot. More of the burden on offense fell to Newton, who was 17 for 30 passing for just 142 yards. Carolina converted 4 of 10 third-down opportunities but was just 2 for 8 after its first possession of the game.
Carolina, which had 10 players named to the Pro Bowl last week, took the opening kickoff and marched 80 yards in 11 plays, with Newton finishing the drive with an 8-yard touchdown run. It appeared that another rout of Atlanta was coming.
After he crossed the goal line, Newton had a protracted end zone celebration, which included pretending to rock a baby in his arms.
The Falcons had been insulted by Newton’s histrionics in their previous loss, and this display fueled even more resentment. Falcons linebacker O’Brien Schofield said the Panthers had posed for a team picture and pranced in celebration with time remaining in that game.
“It was very disrespectful to a lot of us, and it definitely sparked something for us,” Schofield said. “Cam Newton was running up and down the sidelines celebrating with the fans before it was over. There were none of those antics today.”
Instead of antics, there was an acrobatic move by Jones, a fifth-year wide receiver, who caught nine passes for 178 yards.
The Falcons were trailing by 10-7 in the third quarter when Ryan was forced left out of the pocket, motioned for Jones to go deep and then threw the ball high down the sideline. Jones was sandwiched between linebacker Luke Kuechly and safety Kurt Coleman, but he leapt and reached over Kuechly, snatching the ball with two hands. He then turned and dashed down the sideline for a 70-yard scoring play.
There were plenty of noisy Carolina fans in the Georgia Dome, but it was finally apparent that this was a home game for Atlanta as the Falcons’ fans erupted at their team’s sudden 14-10 lead.
“I think I might have jumped a little too early,” Kuechly said.
Ryan said of Jones, “I really don’t feel like there’s anybody in the league who’s better in that situation than him.”
Ryan finished with 23 completions on 30 attempts for 306 yards.
Carolina pulled to 14-13 on Graham Gano’s 47-yard field goal with 7 minutes 59 seconds left in the game. Atlanta’s Shayne Graham kicked a 37-yard field goal with 2:23 seconds remaining to make it 17-13.
Newton had two chances to rally his team, but Falcons defensive linemen Vic Beasley Jr. and Ra’Shede Hageman would not give Newton any peace. The Panthers’ first turn with the ball in the final period ended after six plays with Carolina giving the ball up on downs at its 37.
Atlanta could have run all but 15 to 20 seconds off the clock, but in a bizarre sequence, the Falcons stopped the clock by committing three penalties. Graham kicked a 54-yard field goal to make it 20-13, but Newton still had 1:30 to keep the unbeaten season alive.
But on the second play, Newton was stripped of the ball by Beasley. It was recovered by defensive end Adrian Clayborn, and the Panthers were denied their chance at a perfect season.
An earlier version of this article reversed the identities of the teams’ kickers in one instance. It was the Falcons’ Shayne Graham who kicked a 54-yard field goal to give Atlanta a 20-13 lead, not Graham Gano, who is the Carolina Panthers’ kicker.