KANSAS CITY, Mo. -- Tyrann Mathieu didn't laugh at the suggestion. He didn't smile or find the least bit of humor in the notion that maybe the Kansas City Chiefs are becoming a team known for big-play defense instead of high-scoring offense.

"I don't know," the straight-faced safety said after the Chiefs' defense led the way in a 40-9 victory over the Oakland Raiders. "We've got to stick to the process. ... We're constantly chasing improvement. We want to be our very best when it matters the most."

Games haven't been any bigger for the Chiefs this season than Sunday's against the Raiders. The Chiefs' win was a huge step toward locking up their fourth straight division title. They now lead the Raiders by two games with four to play, and thanks to their season sweep they also hold the tiebreaker.

They have their defense to thank for that. The Chiefs intercepted Oakland's Derek Carr twice in the first half Sunday, with safety Juan Thornhill returning his pick for a touchdown. The Chiefs also had a key fourth-down stop.

The Raiders didn't score until the fourth quarter, after the Chiefs led by 31 points, and didn't get their only touchdown until the game's final minute.

It's not an anomaly. The Chiefs also played well defensively in Week 10, intercepting Chargers quarterback Philip Rivers four times. But the game against the Raiders has them believing it's for real.

"This game means a lot, honestly," Thornhill said. "Guys are just coming together. When you come together you're going to play a lot better because you know what the guy next to you is doing. That's going to allow you to play way faster.

"Guys are focusing more on their job instead of trying to make other plays that's not theirs. When you focus on your job and everyone does their job, you make plays."

Against the Raiders, the Chiefs had just 259 yards on offense, their lowest total of the season by 50 yards. The Chiefs also struggled for much of the game on offense against the Chargers. This comes a year after leading the league in yards and points per game while their defense consistently let them down in big moments, such as the overtime playoff loss to the New England Patriots.

It's a different world for the Chiefs now that their defense is carrying its fair share and more.

"We've been kind of known these last few years of scoring all these points and putting up all these numbers," quarterback Patrick Mahomes said. "But when your defense is playing like that and they're getting the ball back to you it's about not trying to turn the ball over and about scoring points whenever you get the opportunity to.

"It was cool when you looked up [at the scoreboard] and I felt like we had scored only a couple of times and it was, like, 31-0."

Having a bye ahead of the Oakland game didn't hurt. The Chiefs implemented a 4-3 defensive scheme this season under new coordinator Steve Spagnuolo to mixed results. Mathieu said the Chiefs used the extra time to refocus on areas that needed improvement, and the coaches challenged the defense to play better than they did against the Chargers.

"The system isn't new anymore," said Mathieu, who had an interception on the game's first drive to set up a Chiefs touchdown. "We're in December. I think everybody's got a good feel for what they need to do, what they can do and what they can't do. We've got a long way to go, but I like what we're putting on tape.

"From this point going forward, I think it's important to play defense. I think every team that makes the playoffs, it's going to be about what their defense can do."

A better challenge for the Chiefs' defense should come next Sunday against the Patriots in New England. While the Chargers and Raiders are near the bottom of the league in scoring, the Patriots were fifth heading into Week 13.

"This week of practice will really be about discipline, assignment discipline, technique discipline, because that's what the Patriots are going to do," Mathieu said. "They're going to run the ball, they're going to throw screens, they're going to wait for you to get out of your gap, they're going to wait for a deep safety to not be deep.

"It starts with me this week in practice, getting our guys ready, setting the tempo early in the week, letting them know we've got a big game this week."