Smith found Vernon Davis on a 42-yard scoring strike less than 4 minutes into the game and connected with Josh Morgan and Brian Westbrook before the first half was over, staking the 49ers (5-8) to a 27-7 lead.
Smith went 17-of-27 for 255 yards and no interceptions. Six passes went to Westbrook for 87 yards as San Francisco kept its playoff hopes in the NFC West alive.
Dashon Goldson returned an interception 39 yards for a touchdown -- one of five turnovers yielded by Seattle.
Matt Hasselbeck connected on 27-of-42 pass attempts for 285 yards and two scores for the Seahawks (6-7), but was picked off four times.
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