The New Orleans Saints could have clinched a playoff berth and moved a step closer to winning the NFC South with a victory in St. Louis on Sunday.
But the Rams, who have given the Saints trouble in the past, continued to do so again on Sunday.
St. Louis outscored New Orleans 17-0 in the first half and held on despite a frantic Saints rally for a 27-16 victory.
New Orleans (10-4) and Carolina (10-4), which defeated the New York Jets 30-20, are tied for first place in the NFC South with two regular season games remaining.
The Saints play at the Panthers on Sunday.
The Saints struggled from the start as quarterback Drew Brees threw two interceptions in the first quarter that led to two touchdowns for the Rams and a 14-0 lead.
The Rams increased their lead to 17-0 after Greg Zeurlein hit a 31-yard field goal in the second quarter.
St. Louis increased its lead to 24-3 when running back Zac Stacy ran through the Saints defense for a 40-yard touchdown run with 4:10 left in the first half.
The Saints scored their first touchdown of the game when Brees scored on a 1-yard plunge to make the score 27-9 with 11:25 remaining in the game. Pierre Thomas was shotpped short of the goal line on a run for the two-point conversion.
Brees threw a 5-yard touchdown pass to receiver Marques Colston to make the score 27-16 with 3:07 remaining.