Sam Bradford picked up only 205 yards on 8-of-17 passing efficiency with a pickoff but also hurled a two touchdowns as St. Louis (4-6-1) won for the first time since they last faced Arizona on Oct. 4.
Steven Jackson piled up 139 yards on 24 carries in the Rams' victory.
Cardinals quarterback Ryan Lindley logged 312 yards on 31-of-52 attempts but was intercepted four times in all in his first NFL start.
Lindley got the nod behind center after John Skelton proved ineffective during the Cardinals' skid.
Beanie Wells scored a pair of rushing touchdowns for Arizona (4-7).