This is bigger than scrounging for a late-season win. Bigger even than keeping alive hopes of winning the NFC West.

Sunday’s anticipated showdown is about reclaiming mojo. The credibility of the 49ers is at stake.

It’s not that San Francisco needs to prove anything to the media. This is not about justifying the rabid belief of its diehard fans. This is one of those look-yourself-in-the-mirror things.

San Francisco elevated itself to elite status by bullying teams. Wearing machismo on their sleeves, the 49ers pounded opponents into submission.

So far this season, they’ve merely feasted on mediocrity. No doubt, you have to be a pretty good team to be 8-4. But the 49ers are better than pretty good. They’re supposed to be, anyway. That is why their eight wins pale in comparison to their four losses.

Each time the 49ers have lined up against teams that aren’t holistically inferior, teams they couldn’t just dominate with force and talent, they have lost. To Indianapolis. To Seattle, embarrassingly. To Carolina. To New Orleans. For whatever reason, they haven’t gotten it done.

San Francisco’s eight wins are against teams that currently boast a combined record of 30-53-1. The only winning team the 49ers have beaten is Arizona.

It’s got to be hard to poke your chest out and mean it when your most worthy victim is led by Carson Palmer. Hard for the tough talk to be sincere when you lose to every team that pushes back.

The 49ers’ mission has changed. Once a favorite for home-field advantage, they now need to get hot. How do you do that when you’re 0 for 2013 against the really good teams you’ve faced?

This is about re-establishing confidence. No better way to do it than by humbling Seattle.

The Seahawks are sitting in the chair that used to belong to the 49ers. They took it by force Sept. 15 when they slaughtered the 49ers in the Pacific Northwest. That was a long time ago, but bullies don’t forget being hit back.

The psychological edge the 49ers need to succeed, to make this season everything it was supposed to be, is on the line Sunday.

The defense has been on a mission to reclaim that physical moxie. Three of the past four opponents have been held to 13 points or fewer. No team has scored more than two touchdowns since Arizona nearly two months ago, and that was in a blowout.

Now, imagine the wonders that would be worked by shutting down Russell Wilson. Imagine the 49ers’ swag if they can beast on Marshawn “Beastmode” Lynch. Lynch had 98 yards in the last meeting, coming within 2 yards of a fourth consecutive 100-yard game against the 49ers.

Yes, Michael Crabtree is back. But imagine what would it mean for the psyche of the 49ers heading into the homestretch if Frank Gore and the offensive line has its way with that Seattle defense.

Niners Nation wouldn’t mind Crabtree or Anquan Boldin stuffing a few touchdowns in the mouth of Seattle cornerback Richard Sherman. But nothing would send as strong a message, nothing would announce “we’re back,” like a good ol’ 49ers pound-and-ground.

Yes, Joe Staley is out, and Mike Iupati is looking iffy for Sunday. Losing two Pro Bowl linemen is a big blow. And if Seattle follows the latest blueprint on containing San Francisco, it’ll have eight or nine players in the box looking to take away the 49ers’ staple.

Damn the consequences, says Gore.

“I don’t care,” he said this week.”We’ve still got to get it done.”

Remember the last time Seattle came to town? Gore rushed for 131 yards, Wilson had a QB rating closer to his age, and the Seahawks lost a 13-6 fistfight.

The 49ers need another one of those. Even if they lose Sunday’s game, they need to walk away having proven to themselves they still can run with the big boys. Seattle needs to at least be bloodied and thanking the heavens it survived with life and limb.

That’s the way San Francisco gets that Super Bowl-caliber confidence back, which is even more important than waking up Monday at 9-4. Without it, they’ll need to start dodging mirrors soon.

Contact Marcus Thompson at mthomps2@bayareanewsgroup.com.