Hasselbeck hit Bobby Engram for a 17-yard touchdown in the first quarter to give Seattle (3-1) a 10-0 lead. He connected with Marcus Pollard for a 14-yard TD that made it 20-0 early in the third quarter.
Josh Brown booted three field goals for the Seahawks while Deion Branch caught seven passes for 130 yards. The Seattle defense had six sacks.
San Francisco (2-2) quarterback Trent Dilfer completed only 12-of-33 passes for 128 yards and was intercepted twice by Marcus Trufant, after starter Alex Smith was knocked out of the game with a shoulder injury on the 49ers’ first drive.
Joe Nedney scored San Francisco’s only points with a 43-yard field goal with 4:36 to play in the third.