Lynch carried the ball 26 times to back rookie quarterback Russell Wilson, who completed 15-of-20 passes for 151 yards and a score in nailing down his first career victory.
Seattle (1-1) rebounded with a decisive win after dropping its season opener last week to the Arizona Cardinals.
Dallas (1-1) was led by Tony Romo, who piled up 251 yards with a touchdown and an interception on 23-of-40 efficiency.
The Seahawks defense held DeMarco Murray to 44 yards on 12 carries.
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