SAN FRANCISCO — A switch of quarterbacks named Smith did wonders for San Francisco.
Alex Smith threw for 255 yards and three touchdowns in a triumphant return to the starting lineup following a five-game absence, and the 49ers improved their once-slim playoff hopes with a 40-21 victory over the NFC West rival Seattle Seahawks on Sunday.
The Niners muddled up the ugly West race even more with a surprisingly lopsided win.
San Francisco (5-8) moved within a game of division leaders Seattle (6-7) and St. Louis (6-7). The 49ers looked much more like the team that was predicted to win the division after an unbeaten preseason — not the bunch that began 0-5.
Matt Hasselbeck went 27 for 42 for 285 yards and two TDs, but threw four interceptions and lost a fumble as Seattle had turnovers in five of six possessions during one stretch.
Vernon Davis caught five passes for 70 yards and a 42-yard catch-and-run TD, Josh Morgan made a 15-yard touchdown reception and Brian Westbrook hauled in a 62-yard touchdown pass for his longest career TD catch and longest play from scrimmage since 2006. Westbrook wound up with six catches for 87 yards.
Alex Smith matched a career high by throwing for three touchdowns for the fifth time. The No. 1 overall draft pick in 2005 was back behind center in place of Troy Smith, who went 3-2 during his stint as San Francisco’s starter.
Not only is Smith playing for a job next season, he might be helping coach Mike Singletary save his.
Dashon Goldson made a 39-yard interception return for a touchdown on the third play of the second half.
This was a far cry from the rivals’ matchup in Week 1, when the Seahawks won 30-6 and San Francisco failed to reach the end zone. Singletary thanked first-year Seahawks coach Pete Carroll afterward for the whipping.
Jeff Reed kicked four field goals Sunday for the 49ers, who had already reached their season high in points by halftime with a 30-7 lead. It was the Niners’ biggest first half since scoring 35 in a 35-16 home win over the Rams on Nov. 16, 2008.
Leon Washington returned a kickoff 92 yards for a touchdown late in the third quarter — the highlight of the day for the Seahawks, who lost for the fifth time in seven games after a 4-2 start.
Deon Butler caught a late 2-yard touchdown and seriously injured his right leg. It appeared Butler broke his leg moments after he caught a 2-yard touchdown pass upon being hit by Phillip Adams. This is another tough blow for the Seahawks, who already were playing without top receivers Mike Williams and Ben Obomanu.
Medical personnel placed a vacuum splint on Butler’s lower leg before taking him for an X-ray. He was quickly transported to Stanford Hospital.
San Francisco is trying to avoid missing the playoffs for the eighth straight season, but realizes it still has an uphill climb to get there.
The 49ers have a quick turnaround to play at San Diego on Thursday night.
Singletary certainly will stick with Alex Smith, who hadn’t played since separating his non-throwing left shoulder Oct. 24 at Carolina — though the coach has said his starter will be determined on a week-to-week basis. Alex Smith has experience running this offense and allows the 49ers to utilize their entire playbook.
Alex Smith was booed after their first play from scrimmage, an incomplete pass intended for Delanie Walker — then again moments later after another incompletion. Smith then hit Davis on a 22-yard gain then the touchdown three plays later for a 7-0 lead.
Seattle tied the game on its second offensive series, when Hasselbeck found a wide-open Ruvell Martin for an 11-yard TD.
Reed’s 33-yard field goal as the first quarter ended barely cleared the crossbar for a 10-7 lead, then he kicked a 44-yarder at the 10:31 mark of the second quarter. His other two went 22 and 36 yards.
Takeo Spikes intercepted a pass by Hasselbeck on the Seahawks’ opening drive of the second quarter, coming down with the ball after fellow linebacker Manny Lawson tipped it off Michael Robinson’s hands.
Hasselbeck, who completed seven of his initial eight throws, is still one victory from tying Dave Krieg as Seattle’s winningest quarterback. Krieg won 70 games from 1981-90.