Now, after a long trip home following their 41-34 victory, the Niners (10-3-1) must play a second straight game on the Sunday night prime-time stage when they visit Seattle trying to wrap up a second consecutive NFC West crown.

“This is a huge win for us,” left tackle Joe Staley said. “With Seattle winning, we had to win this game. It felt like a playoff game.”

The Seahawks (9-5) have scored 108 points in their last two games — a 50-17 win at Buffalo on Sunday after a 58-0 rout of Arizona a week earlier — so everybody knows it will be another important test for San Francisco’s stingy defense.

The 49ers certainly have some momentum coming down the stretch in late December as they gear up for another postseason run, one they hope goes one step further than their overtime loss to the eventual champion Giants in last January’s NFC title game.

Beating Brady and Co. didn’t hurt as San Francisco prepares for the games that matter most.

“It is real big and it says a lot about this team to travel across the country and play a late game, and in their environment with cold and rain,” said cornerback Carlos Rogers, who intercepted a pass by Brady midway through the first quarter and ran it back 53 yards to the Patriots 5. “I am pretty sure everybody picked us to lose. It just seems every time we get on Thursday night, Sunday night, or Monday night, we show up and that is what we did. We stuck with our plan and we knew it was going to be tough coming in. We just had to stay poised, stay fighting and play physical. … Offense put up the points and we got the win.”

Several of the 49ers said Sunday’s game felt like a preview of the playoffs — with Brady and the high-flying Patriots’ offense against San Francisco’s opportunistic defense.

And this week should be no different when the Niners play in what is largely considered the loudest road venue in the NFL — against a team fighting to secure a playoff spot. Harbaugh is all for his team being tested late in the season.

“I think that could be a positive,” the coach said Monday. “I think the thing that the players were feeling and probably anybody that was watching it was feeling was that they’re two teams that — two very good teams, two hard-hitting teams — have a lot of pride in how they play, really came out to see who’s better, and wanted to be better and wanted to win that game. And it showed. This game will be the same, I really believe that. We need to prepare.”

San Francisco turns its focus to slowing down a surging Seattle team led by rookie quarterback Russell Wilson while also keeping hold of the NFC’s No. 2 seed in an effort to secure a first-round playoff bye. Atlanta holds the top spot at 12-2, while Green Bay is right behind the Niners at 10-4.

Running back Frank Gore considered the game at New England a must-win, and will treat this week the same way.

“Yeah, we had to, we had to,” Gore said. “We put ourselves in a situation where we had to win out and we knew that it was going to be tough coming down here and getting a win against a great team, especially a team that had a great game last week.”

Harbaugh was quick to credit his coaching staff Monday for using the cross-country flight home not to sleep or watch a movie but rather study game film, from Sunday night and also some preliminary work on the Seahawks. San Francisco beat Seattle 13-6 in the 49ers’ division opener on Oct. 18.

Harbaugh watched Sunday’s game again, noting that the Niners had chances to get off the field during the Patriots’ stretch scoring 28 unanswered points.

“Watched the entire game, offense, defense and special teams and work on Seattle,” Harbaugh said. “It’s a pretty impressive thing. I’ve never been associated with a team like this, where the coaching staff is — it’s like a work station in the back part of the plane. The computers are on, nobody is watching movies and not a lot of sleeping going on. Really impressed with our guys the way they do that. And the players too, they had laptops and were watching the game in groups and then eventually fell off to sleep.”

Defensive tackle Justin Smith underwent an MRI exam on his injured arm, which forced him to miss the fourth quarter Sunday night.

“It’s really going to be how he is today, tomorrow, Wednesday, before we know anything,” Harbaugh said.

Smith has started 185 straight games dating to his rookie season in 2001. The streak ranks third among NFL players, behind Ronde Barber (213) and London Fletcher (197).

“I’m going to do everything I can to play,” Smith said after the game.

Notes: The 49ers re-signed WR Chad Hall to the practice squad. … Harbaugh said San Francisco would fill the final spot on the 53-man roster this week. When asked about struggling kicker David Akers, Harbaugh insisted he will remain the guy — for now, at least. Any possible changes ahead? “No, not at this time,” he said. Akers missed wide left on a 39-yard attempt Sunday.