Smith was 17-for-27 for 255 yards and three touchdowns without an interception. Kicker Jeff Reed, who joined the team before last weeks game, was 4-for-4 on field goal attempts for the now 5-8 Niners, only one game off the division lead, held by both Seattle and St. Louis. The Rams also lost on Sunday.
Brian Westbrook caught six passes for 87 yards and a score while rushing for 23 yards on nine carries. Vernon Davis accounted for 70 yards and a TD on five catches in the win.
“We’re a young team and today was big for us,” 49ers coach Mike Singletary said. “But at the same time, today means nothing if we don’t play well next week. We have very little room for error, and we have to understand that.”
Matt Hasselbeck threw for 285 yards with two scores on 27-of-42 passing, but his four interceptions were the deciding factor for Seattle (6-7), which has lost three of four.
San Francisco capped the game’s first drive when Smith hit Davis across the middle for a pass that the tight end took 42 yards to the end zone. After the teams traded punts, Hasselbeck connected with Ruvell Martin for an 11-yard score to knot the game at seven.
The 49ers’ defense stepped up during the next 2 1/2 quarters and led the charge to 33 consecutive points. Reed connected on a 33-yard field goal in the closing seconds of the first quarter to put San Francisco up, 10-7.
Seattle had the ball at midfield in the opening minutes of the second quarter, but Hasselbeck was picked off by Takeo Spikes at the Seahawks’ 47. The 49ers added another Reed field goal, this time from 44 yards out, to move ahead, 13-7, with 10:31 left in the quarter.
Three plays later, deep in Seattle territory, Hasselbeck was sacked and fumbled for his second turnover of the game. Smith then hit Josh Morgan for a short strike, and he broke two tackles en route to a 15-yard touchdown and a 20-7 49ers lead.
The 49ers widened the gap to 27-7 when Smith connected with Westbrook for a 62-yard score down the middle of the field with 1:50 left in the half.
The forgetful day for Hasselbeck continued when he was picked off for the second time, this time on a 2nd-and-20 at the Seattle 10. Reed added a 22- yarder on the final play of the half to give San Francisco a 30-7 lead.
The Seahawks received the second half kickoff, but Hasselbeck was picked for the third time of the day, and Dashon Goldson returned the interception 39 yards to the end zone to put San Francisco up, 37-7.
Reed added another 36-yard field goal in the final minutes of the third quarter to cap a seven-play, 51-yard drive. Leon Washington ended the Seattle drought as he took the ensuing kickoff 92 yards to make it a 40-14 game with 3:18 left in the third.
The Seahawks had a productive drive going in the opening minutes of the fourth quarter, but after working the ball down to the 49ers’ 19, an offensive holding penalty pushed Seattle back to the 29. Olindo Mare attempted a 43-yard field goal just before the nine-minute mark, but the kick went wide right.
Seattle added the game’s final score when Hasselbeck capped a 9-play, 80-yard drive on a two-yard strike to Deon Butler with 1:55 left on the clock.
“It’s playoff mode right now,” Smith said. “It was a must-win game. We knew that all week—our backs against the wall.”
The Niners have a big Thursday night game this week as they travel to San Diego.