KANSAS CITY, Mo. -- When the Kansas City Chiefs failed to make important fourth-quarter stops in four losses during October and November, the pressure on new defensive coordinator Steve Spagnuolo tightened.

The defense that Spagnuolo was brought in to fix hadn't shown much improvement from the previous year when it was a liability. With an offense as explosive as the Chiefs', the defense was once again threatening to ruin a good thing.

But the Chiefs anticipated some tough times early in the season, when they were trying to mesh many new elements while changing from a 3-4 to a 4-3 defense. Spagnuolo resisted the temptation to veer away from his plan and stuck to it. The results over the past five games are his reward.

The Chiefs have allowed 48 points during that span, or less than 10 per game. They've won five straight games and are 11-4 heading into Sunday's regular-season finale against the Los Angeles Chargers at Arrowhead Stadium (1 p.m. ET, CBS).

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"I think there's always a little bit of that when we struggle in anything in life," said Spagnuolo of doubt. "It could be anything, life, whatever, but certainly in football. What I have learned, because there have been a couple of times when we've felt this way, I've always found it best to believe and trust in what you're doing. If you didn't believe in it and trust in it, you shouldn't have been doing it in the first place.

"We talked a lot about trust. We started talking about 'Trust our way to improvement,' which is the way we put it, the way the coaches fed it to the guys. To the guys' credit, they embraced it."

Between a new defensive coaching staff, a new base system and a lot of new players, Spagnuolo, 60, had much to accomplish in a short amount of time after joining the Chiefs.

But he never flinched.

"He's done a phenomenal job of teaching his defense in a short period of time and then getting the results from that," coach Andy Reid said. "He's got the guys believing in that system. That's hard to do when you switch over."

Spagnuolo was a natural selection for Reid to replace former defensive coordinator Bob Sutton, who was fired after six seasons with the Chiefs. Spagnuolo was an assistant for Reid for eight seasons with the Philadelphia Eagles.

Since then, Spagnuolo had some good times and some bad. He was the defensive coordinator for the Super Bowl-winning New York Giants in 2007. But he failed in a three-season stint as head coach of the St. Louis Rams with a 10-38 record from 2009 to 2011. Then his defenses were among the worst in the league during a season with the New Orleans Saints (2012) and a subsequent time with the Giants (2015-17).

After a year away from football, Steve Spagnuolo didn't have a great start with the Chiefs' defense, but that has changed dramatically in the past five games. Scott Winters/Icon Sportswire

He took a season off from coaching last year, a first since his career began in 1981 as a graduate assistant at the University of Massachusetts. He traveled to practice sessions around the league, including those of the Chiefs, in search of new ideas.

"I'm glad I did it," he said. "I found it to be challenging and rewarding. The challenge was missing football, missing the camaraderie of coaches and players, not being at training camp.

"The rewards were to sit back, see a big-picture view of the NFL and the game of football as opposed to being in these buildings during the season and having the blinders on of just the team you're going to play. I just thought a big-picture view of the league, the game of football ... I have oodles of notes."

Spagnuolo and Reid hired a defensive coaching staff of Brendan Daly (line), Matt House (linebackers), David Merritt and Sam Madison (secondary). All had either coached or played for Spagnuolo.

"It tells you something about Spags with the people that came here with him, that we were able to recruit here," Reid said. "These are guys that he's worked with before and they have enough trust in him to come here. That tells the players that maybe this is a pretty good thing right here."

Changing the defense was still an ambitious project.

"It's to be expected anytime you change schemes there's a learning curve and an adjustment curve and a curve for the coaches to find out the best way to play these players as a unit," said Denver coach Vic Fangio, whose Broncos lost twice to the Chiefs this season, scoring a total of nine points.

"Usually that happens at some point midway through the season or just past the midway point and that seems to be what's happening to them."

The Chiefs also invested heavily in their defense by signing free agents like safety Tyrann Mathieu and end Alex Okafor, trading for end Frank Clark and drafting safety Juan Thornhill.

All had an impact this season, but none bigger than Mathieu, who has played well and been a locker-room leader.

"Me and Spags, I think we feed off of each other," Mathieu said. "I feel like I'm an extension of him on the football field -- just trying to understand really what he wants to get done, how he sees us playing the game plan, and for me, just being the middle man, trying to relate that to our guys so they can understand.

"We understand when he speaks, it's coming from a great place. He's a Christian man. He has strong values. On top of that, he's a pretty good football coach. One of the things I pick up on with anybody standing in front of the room is, 'Can they command the room? Can he coach every position in the room?' I think Spags can do all of that."

Spagnuolo is more hands-on than most coordinators on the practice field. At one time or another he has pulled most -- if not all -- defensive players aside for one-on-one instruction.

"Sometimes it's about tackling, sometimes it's about ball awareness," linebacker Damien Wilson said. "It can be about anything."

Spagnuolo hammered away in defensive meetings early in the season for the players to keep believing, even as things weren't going well. They listened to him, in part because of what he accomplished before joining the Chiefs.

"He's been where we all want to go," Wilson said of the Super Bowl. "That gives him some credibility with the guys.

"He kept saying it was like we were digging a well. If we stopped in the middle, we were never going to get to the water. So we kept digging. It seems to be working."