The Seahawks dominated the 49ers from the start in rainy Seattle to remain unbeaten at home and move within half a game of division leaders San Francisco.
The 49ers entered the game with a chance to clinch the division but found themselves on the wrong end of a beating by surging Seattle (10-5), who have won four straight games including the last three by a combined 120 points.
San Francisco (10-4-1) can still claim the crown with a home win over Arizona while Seattle need to beat St Louis and hope for a 49ers loss to leapfrog their rivals.
"When we wake up tomorrow we're still a half-game up on the division," shellshocked 49ers coach Jim Harbaugh told reporters. "I know what to expect in terms of how our team will handle (the loss)."
Marshawn Lynch triggered the rout with two touchdowns in the first quarter before Richard Sherman returned a blocked field goal attempt 90 yards to give Seattle a 21-0 lead at the start of the second.
Rookie quarterback Russell Wilson had touchdown passes in all four quarters, finishing the game with four, to emphatically outplay San Francisco's signal caller Colin Kaepernick.
Wilson is one touchdown pass short of tying Peyton Manning's NFL rookie record of 26.
"My goal is just to continue to grow. I'm on that constant quest for knowledge and our team is too," Wilson said. "We've had a great year so far, we have to keep moving forward we have a lot to look forward to."
Kaepernick often appeared flustered because of the deafening crowd noise and struggled to break down a stout Seahawks defense which is dealing with injuries to their defensive backs but was still too strong for the 49ers.
"We have amazing depth," Sherman said. "We have great players that are going to be starters in this league. They stepped up and were big for us tonight."
Seattle may have to rely on their depth more than ever as Sherman is currently appealing a four-game suspension for violating the league's performance enhancing drug policy.
It was no only San Francisco's pride that took a beating on Sunday. Tight end Vernon Davis (concussion) and receiver Mario Manningham (knee) were both knocked out of the game.
Seattle's Lynch finished with 111 yards on the ground as the Seahawks gave the 49ers a taste of their own medicine with a bruising ground game.
Wilson threw a six-yard scoring pass to Anthony McCoy in the second quarter, and touchdowns of four and six yards to Doug Baldwin in the third and fourth to put Seattle out of sight.
The stunned 49ers could only manage two field goals in the first half and a touchdown reception Delanie Walker in the final minutes with the game out of reach.
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