SEATTLE -- The 49ers still see themselves as a playoff-bound team, which they are. They still think they'll repeat as NFC West champions, which they can do in the regular season's final hours next Sunday.
But Sunday night, they weren't any good, losing 42-13 to a Seattle Seahawks team that showed no sign of being intimidated on their home turf, where they remain unbeaten this season.
"It was a punch in the face," 49ers cornerback Carlos Rogers said of the 49ers' most lopsided loss since 2009. "But the thing about it is we still have a chance to win the division, and we're already in the playoffs."
The 49ers (10-4-1) can claim their second straight NFC West title next Sunday by beating the Arizona Cardinals (5-10) at Candlestick Park, or by having the Seahawks (10-5) fall to the visiting St. Louis Rams (7-7-1).
"Our destiny is still in our hands, and that's what's most important," linebacker Patrick Willis added.
Both the 49ers and Seahawks are assured playoff berths. The 49ers clinched at least a wild-card spot a week ago after outlasting the New England Patriots 41-34. The Seahawks earned their playoff ticket with Sunday's prime-time win.
But the 49ers no longer own the NFC's second-best record, which would merit a first-round bye. The Green Bay Packers (11-4) now are in the No. 2 slot behind the Atlanta Falcons (13-2). The Packers can secure that seed next Sunday by either winning at the Minnesota Vikings (9-6) or having the 49ers lose to the Arizona Cardinals (5-10)
"If we don't get the No. 2 spot, we've got to go another route," running back Frank Gore said.
The 49ers defense clearly struggled without the leadership and presence of Justin Smith, a defensive-line mainstay whose serious elbow injury sidelined him for the first time in 190 games.
On the offensive side, the 49ers saw two key players vanish during their long-shot comeback attempt: tight end Vernon Davis (concussion) and wide receiver Mario Manningham (knee; X-rays were negative).
On the flip side, Seahawks coach Pete Carroll celebrated the "terrific win" by magnifying what it meant to triumph for the first time in four meetings against 49ers counterpart Jim Harbaugh, his old Pac-10 rival.
"Those guys have been winning like crazy the last couple years," Carroll said. "They have a terrific football team. ... I take a lot of pride in the fact that we played like that against this team and these coaches."
In spoiling Harbaugh's 49th birthday, the 49ers fell behind 21-0 less than a minute into the second quarter.
That third Seahawks' touchdown set the night's tone. The 49ers were settling for a 21-yard field goal attempt by David Akers, but Red Bryant blocked the kick and Richard Sherman returned it 90 yards for a game-breaking touchdown.
"The momentum changed right when they blocked the field goal," linebacker Ahmad Brooks said. "I don't want to say it sealed the deal, but it gave them confidence to think (the 49ers) are not what the world thinks (the 49ers) are."
By the time Sherman intercepted a Colin Kaepernick pass in the end zone early in the fourth quarter, the Seahawks already held a 35-6 lead. The 49ers hadn't been outscored this badly since a 45-10 home loss to the Atlanta Falcons on Oct. 11, 2009.
Seahawks quarterback Russell Wilson threw four touchdown passes for the first time in his sensational rookie season, and his elusiveness in the pocket often made 49ers pass rushers look daffy.
Wilson got sacked only once, and that was for no yards by Isaac Sopoaga. Aldon Smith's season sack total held steady at 19½ for the second straight week, dropping him a sack behind league leader J.J. Watt of the Houston Texans.
Marshawn Lynch, an Oakland native and Cal product, scored touchdowns on the Seahawks' first two possessions to stake them to a 14-0 lead.
The Seahawks didn't cool off under the rainy skies. They converted 11 of 12 third-down opportunities before backup Matt Flynn knelt down on their final third-down snap as time expired.
"We didn't win third down enough and we didn't do good enough," said Harbaugh, who's offense was 3 of 11 on third-down conversions.
It was the largest deficit in Harbaugh's two-season 49ers tenure. It marked the second loss in six starts by Kaepernick, who completed a career-low 52.8 percent of his passes (19 among a career-high 36 attempts for 244 yards).
"It's not our first loss," Harbaugh added. "We'll wake up tomorrow with a half-game lead on the division. Our hand will be on the dial to take care of business next week."
Under Harbaugh's reign, the 49ers haven't lost back-to-back games. This season, they haven't won three in a row, however, and that is something they'll have to do in the playoffs if they want to win their first Super Bowl since the 1994 season.
"We're picked to go to the Super Bowl," Rogers said, "but that's not promised, like I keep telling guys."