Tony Romo and DeMarcus Ware helped Dallas end its December doldrums and the Cowboys held off a frenzied rally by the Saints for a 24-17 victory Saturday night.
The loss by the Saints (13-1) left the Indianapolis Colts (14-0) as the NFL's only unbeaten team this season.
The high-scoring Saints trailed 24-3 going into the fourth quarter, then scored two quick touchdowns.
After Dallas kicker Nick Folk watched his 24-yard field goal try clang off the right upright shortly before the 2-minute warning, Brees got a final chance to tie it.
Brees moved the Saints into Dallas territory. But on second down, Ware sacked Brees and forced a fumble that was recovered by the Cowboys with 6 seconds left.
Romo passed for 312 yards, including a 49-yard touchdown to Miles Austin, who went over the 1,000-yard mark in receiving yards this season.
Ware returned from a neck injury that left his status in doubt and was part of a relentless Dallas pass rush that pressured Brees all night.
Marion Barber had two short touchdown runs for the Cowboys (9-5), who ended a two-game skid and proved they were good enough to beat the top team in the NFC in front of a charged-up, hostile crowd.
The Cowboys' troubles in December (3-7 under coach Wade Phillips) had been well documented, but this win provided a dramatic boost to their playoff chances.
Romo connected with Austin, and Marion Barber later scored from 3 yards as the Cowboys took a quick 14-0 lead in the first quarter.
Folk added a 44-yard field goal three seconds before halftime.
Ware, who did not practice all week after suffering a neck sprain that sent him to the hospital six days earlier against the San Diego Chargers, forced a Brees fumble on a sack late in the first half, leading to Folk's field goal.
The Cowboys led 17-3 at the half.
The Saints got on the board when Brees led a 12-play 75-yard drive, completing a 35-yard pass to Marques Colston to the Cowboys 17. The Saints stalled from there, setting up Garrett Hartley's 34-yard field goal.
The Saints lost running back Reggie Bush to an apparent right leg injury in the second quarter. Bush caught a pass in the middle of the field, pulled up, hobbled to the sideline and headed straight to the bench. He did not return in the third quarter.
Brees set a record for career TD passes for a Saints quarterback with 121.