SANTA CLARA — This is it.

George Kittle and Kyle Juszczyk both said they wouldn’t have believed it two months ago if you told them that the San Francisco 49ers would be playing for the No. 1 seed in the NFC on Saturday night. But here they are, after all the injuries and fill-ins filling the stat sheet, at 12-4 and facing their toughest test of the season. With the biggest stakes.

Win, and the 49ers won’t leave Levi’s Stadium, with home-field advantage all the way through the Super Bowl being played here as well. Lose, and the 49ers hit the road next week for the first round of the playoffs, likely in either Chicago or Philadelphia.

“This game is everything,” 49ers safety Malik Mustapha said. “It’s everything that we wanted, everything that we worked for, and now the opportunity is here, so we’ve had a great week of preparation, and now it’s just getting the W.”

The Seahawks (13-3) may be the better team on paper, with the No. 1 defense in EPA per play allowed, one of the NFL’s top five receivers and a running game that has found its legs. But the 49ers have also won six games in a row and have the hottest quarterback in the league in Brock Purdy.

A look at what players and coaches are saying about the biggest matchups on the field Saturday night:

When the 49ers have the ball

The 49ers have the NFL’s most efficient offense since Purdy returned from his turf toe injury in Week 11. They lead the NFL in points per drive (3.4) and TD percentage (41 percent of drives) over that span.

Christian McCaffrey is doing his best Marshall Faulk impersonation, receiver Jauan Jennings has scored at least one touchdown in five straight games and tight end George Kittle is back after missing a week with a tweaked ankle. Meanwhile, Purdy has been just as dangerous with his feet as with his arm.

Seahawks coach Mike Macdonald said the Seahawks may look to scheme things up to keep Purdy in the pocket.

“There’s definitely a balance. He’s doing a great job,” Macdonald told reporters. “There’s a lot of plays where he’s throwing it on time, layering throws over players and seeing defenses before it happens and making you pay that way. He’s obviously making a lot of extended plays and being creative and using his playmaking ability as well.”

The 49ers lead the NFL in third-down conversion rate (51 percent) and have converted 59 percent of their third downs over the last six games.

The Seahawks have the best third-down defense in the league, allowing conversions 32 percent of the time.

“They have elite players at all three levels,” 49ers offensive coordinator Klay Kubiak said. “They’re probably as sound as anyone in terms of their coverages, they bring enough blitzes to keep you honest, and they’re physical, and they tackle, and they do everything well, and it’s just top to bottom.’

Leonard Williams and Byron Murphy II are a load inside up front for Seattle, while DeMarcus Lawrence has been as advertised on the outside since coming over from the Cowboys. Ernest Jones leads the linebackers corps that pursues with an edge, while the Seahawks may have the best secondary in the NFL. Cornerback Devon Witherspoon and rookie safety Nick Emmanwori, who only played four plays in the season-opening loss to the 49ers before getting hurt, are elite playmakers.