SEATTLE -- The 49ers were without the services of injured defensive tackle Justin Smith on Sunday night against the Seattle Seahawks.
And a whole bunch of other 49ers were absent, too.
The surging Seahawks got off to a hot start and the 49ers did not provide much of a challenge in a 42-13 loss in front of a deafening crowd on a drizzly night at CenturyLink Stadium.
It was the largest defeat of Jim Harbaugh's two seasons with the 49ers. Earlier this season, the 49ers lost to the New York Giants by 23 points. The game continued a pattern in which the 49ers never had more than a two-game win streak the entire season. The 49ers have not lost back-to-back games under Harbaugh, who watched as the Seahawks spoiled his 49th birthday with the blowout win.
The 49ers played poorly from the outset. And to make matters worse, two offensive starters exited the game with injuries. Tight end Vernon Davis sustained a concussion after absorbing a brutal -- and illegal -- hit from Seattle safety Kam Chancellor in the first quarter.
Receiver Mario Manningham, who returned to action after missing the two previous games with a shoulder injury, went down in the third quarter with what is feared to be a serious left knee injury. He did not return.
Quarterback Colin Kaepernick and the 49ers' offense struggled to get the ball snapped in the allotted time. The 49ers were flagged twice for delay-of-game penalties in the first half, and they called timeouts to avoid two other penalties in the first 30 minutes of the game.
The loss drops the NFC West-leading 49ers to 10-4-1 and out of the No. 2 spot in the NFC playoffs. The Green Bay Packers (11-4) hold a half-game lead over the 49ers for a first-round bye and a home game in the divisional round. The No. 3 seed would host a playoff game against the NFC's No. 6 seed the weekend after the regular season.
The 49ers can still gain the No. 2 seed with a victory over the Arizona Cardinals next week at Candlestick Park, along with a Packers loss at the Minnesota Vikings.
If the 49ers beat the Cardinals, they will win the NFC West. The Seahawks, who clinched a playoff spot with the victory, can only win the division title with a victory over the St. Louis Rams, coupled with a 49ers loss to the Cardinals.
Manningham's availability for the playoffs is in serious doubt, and Davis must pass the NFL's protocol for concussions in order to return. Davis is required to receive clearance from an independent neurologist before he can take part in football activity.
Chancellor was penalized 15 yards for his hit on Davis, and things only got worse from there. Despite a first-and-goal situation, the 49ers settled for a short field-goal attempt. And that proved disastrous.
Struggling David Akers' kick appeared low, and Red Bryant penetrated against Joe Staley and blocked the field-goal attempt. Richard Sherman scooped up the ball and returned it 90 yards for a touchdown. Sherman continues to play while his four-game suspension for violating the NFL's substance abuse policy is under appeal.
Sherman's touchdown gave the Seahawks a 21-0 lead just 55 seconds into the second quarter. Sherman opened the fourth quarter with an interception of a short Kaepernick pass in the back of the end zone.
In a game matching a pair of young dual-threat quarterbacks, Seattle rookie Russell Wilson had the upper hand.
Wilson completed 15-of-21 passes for 171 yards with four touchdowns and an interception. The rookie quarterback added 29 yards rushing on six carries and watched from the sideline as Matt Flynn handled the final kneel downs to end the game. Meanwhile, Kaepernick completed 19-of-36 passes for 244 yards, with one touchdown, a garbage time connection with Delanie Walker, and one interception. Kaepernick was also the 49ers' leading rusher with 31 yards on seven carries.
Justin Smith saw his streak of 185 consecutive starts come to an end, as he was inactive due to a left elbow injury. Ricky Jean Francois made the start on the defensive line in place of Smith, whose ironman streak began in 2001 as a rookie with the Cincinnati Bengals.
The Seahawks immediately tested Smith's replacement, as Marshawn Lynch scored on a 24-yard touchdown run over the right side of the 49ers' line. Seattle took advantage of a blown coverage as Lynch scored late in the first quarter on a 9-yard pass from rookie quarterback Russell Wilson for a 14-0 lead.
The Seahawks extended their lead to 28-3 late in the second quarter on tight end Anthony McCoy's 6-yard touchdown catch.
Akers ended the half on a good note with a 54-yard field goal to cut the Seahawks' lead to 28-6.
The third quarter did not begin well for the 49ers, as Manningham lost a fumble on a play in which he sustained a left knee injury.
Manningham caught a short pass from Kaepernick. Cornerback Jeremy Lane immediately had him stopped. Linebacker Leroy Hill came in and hit Manningham low, causing Manningham's knee to bend awkwardly. He required assistance to leave the field and was then transported on a cart to the 49ers' locker room for further evaluation.
The Seahawks poured it on in the second half as Wilson threw touchdown passes to Doug Baldwin that covered 4 and 6 yards. Baldwin and Sherman both played for Harbaugh at Stanford.