49ers linebacker details what drives San Francisco's defense

The win sets up a Week 18 showdown against the Seattle Seahawks, where the 49ers can clinch the NFC's No. 1 seed and home-field advantage throughout the playoffs.

Defense plays for injured 49ers teammates

After the final whistle, Fred Warner, working his way back from injury, made his way to Tatum Bethune, who has filled Warner's linebacker role on defense. Bethune had his ups and downs on the night, but he was on the field for the deciding play and nearby when his teammates broke up the potential game-winner.

Speaking with NBC Sports Bay Area's Laura Britt, Bethune said their sidelined teammates have fueled the defense's effort this season, overcoming adversity each week.

"We dedicated ourselves to just do it for [DE] Nick [Bosa], Fred, [DE] Mykel [Williams], and they're supporting us every single day," Bethune said. "And it's just like a slap in the face to them if we go out there and do it halfway. So, we go out there and give it 100%. We know it's on the line."

The 49ers defense knew they had a massive challenge on Sunday night, facing second-year Bears quarterback Caleb Williams, who finished with 330 passing yards and two touchdowns.

"We know their quarterback can make a lot of huge plays, especially in situations like that, in the last play of the game," Bethune said. "And we just had to bold up, and make a play, and get a stop, and that's what we did. And now, we get to celebrate the win for one night, and get back to work."

Bethune recorded a game-high 11 tackles and continues to gain confidence as he settles into the bigger role. Britt asked Bethune to share his biggest area of growth this season.

"Just being confident," Bethune said. "Beginning, when I first started playing, I kind of was second-guessing myself, and being hesitant with calls, and just being myself. And I talked to Fred, and I talked to Coach Johnny Holland, our linebacker coach, and they just told me to be me.

"They brought me here for a reason, and my instincts and my playmaking abilities, and that's just what I did on the field. And we were able to get the dub, and now we just trying to do it again."

Focus locked on Week 18 — and the No. 1 seed

Bethune admitted that earning the NFC's top seed is a constant topic inside the 49ers locker room, but staying focused on taking the season one day at a time is the priority.

"Now we actually get the moment this week, and we're real excited," Bethune said. "We know the Seahawks is a great team, just like the Bears, and we just got to get it done again."

The 49ers will host Seattle on Saturday night, with a chance to secure home-field advantage and make every path to a Super Bowl LX championship run through them at Levi's Stadium.