Lynch's 16-yard scoring scamper in the fourth quarter capped Seattle's scoring. It was his ninth straight game with a touchdown, equaling Steve Alexander's club mark.
Lynch also posted his fifth 100-yard rushing performance in six weeks while leading the Seahawks (6-7) to their fourth win in five games and 13th in 14 meetings with St. Louis.
Tarvaris Jackson completed 21-of-32 passes for 224 yards, including a 29-yard touchdown toss to Doug Baldwin, who made seven grabs for 93 yards.
Sam Bradford managed only 12 completions on 29 pass attempts for 193 yards and an interception for the Rams (2-11), who dropped their fourth straight.