NEW ORLEANS -- The New Orleans Saints suffered the most improbable loss of the season on Sunday when they got steamrolled in their own Superdome 26-9 by the rival Atlanta Falcons.

The Saints were favored by 13.5 points, according to Caesars Sportsbook -- the biggest favorites to lose a game this season.

New Orleans was 7-1 heading into the game, having won six straight. The Falcons were 1-7, losers of six straight. And the Saints were expected to be even more explosive with top offensive players Alvin Kamara and Jared Cook returning from injuries.

Yet somehow the Saints got routed on a day when they couldn't get out of their own way with a total of 12 penalties for 90 yards.

Drew Brees was sacked six times by a Falcons team that entered the game last in the NFL with only seven sacks on the entire season.

"We didn't play well enough to win today -- really against anybody," Saints coach Sean Payton said when asked about warning his team against a letdown. "Shame on us if we can't get those corrections made. And that won't be a problem. ... That's one of those things in this game that creates a little bit of toughness and grit."

Kamara ran for 24 yards on just four carries and caught eight passes for 50 yards. But Payton pointed to the penalties and the Saints' 3-of-12 success rate on third downs as drive killers.

Brees finished the game 32-of-45 passing for 287 yards with no touchdowns or interceptions.

The Saints' costliest penalty was probably a roughing-the-punter call against safety J.T. Gray when the Saints were trailing 20-9 with nine minutes left in the fourth quarter. But they also got flagged three times when they allowed Atlanta to stay on the field for a 17-play touchdown drive in the first half.

A pair of injuries to cornerback Marshon Lattimore and guard Andrus Peat also hurt the Saints.

Lattimore was shadowing Falcons receiver Julio Jones before he left the game in the second quarter with a thigh injury. He never returned despite trying to work himself back into shape on the sideline.

Before Lattimore's injury, Jones was held without a catch. Afterward, Jones caught three balls for 79 yards.

The Saints have three more division games upcoming on the slate, starting with a trip to Tampa Bay in Week 11.