The Denver Broncos did everything right in the first half against the Kansas City Chiefs a few weeks ago, holding Patrick Mahomes and their high-powered offense in check for 30 minutes.
Everything unraveled after the break.
The Chiefs found their rhythm behind their stable of offensive stars, their defense began to stop Broncos rookie running backs, and Kansas City mounted a second-half charge that resulted in yet another victory over its biggest rival in what has become a one-sided series.
Now, the Chiefs (6-1) are ready to go for the season sweep Sunday at Arrowhead Stadium.
"I think both sides will take what they did well a month ago," Broncos coach Vance Joseph said, "but what we did last time won't be good enough to win this time. What we did last time was play good enough football to lose the game. We can't go in with the same plan and mindset."
The mindset for the Broncos (3-4) these days is to build some midseason momentum. They're coming off a 45-10 shellacking of the Arizona Cardinals, and a victory over the front-running Chiefs would go a long way toward positioning them for a playoff run.
No wonder Broncos cornerback Chris Harris Jr. called it a season-changing opportunity.
"It is," added Broncos wide receiver Emmanuel Sanders. "Think about it: Go to Arrowhead, beat these guys, a team that's at the top of our division right now, coming off a big-time game in Arizona. This is a game where we sit back and say, 'OK, was Arizona a fluke or are we really good?' That's what I'm looking forward to seeing."
There's been nothing fluky about the Chiefs' hot start.
Their only loss came in a shootout in New England, and they bounced back in fine fashion by walloping the Cincinnati Bengals 45-10 last week. Mahomes continues to throw touchdown passes by the handful, and his array of weapons has made trying to stop the Chiefs a veritable nightmare.
"You want to score every single time you're out there. That's what we believe in this offense we can do," Mahomes said. "Hopefully we can keep that success going."
That goes for both sides of the ball. The Chiefs' maligned defense played by far its best game of the season last week, holding Andy Dalton and the Bengals' offense to 239 yards total.
"If we can get teams one-dimensional and let the guys on the back end do what they do," Chiefs linebacker Reggie Ragland said, "we're going to have a good shot at winning a lot of games, especially with the offense we got."
As the Broncos head to Kansas City for an AFC West showdown, here are some key story lines:
BARTERING BRONCOS: For the first time in a decade, the Broncos are seen as potential sellers instead of buyers ahead of next week's trade deadline. Prominent names bandied about have included Harris, WR Demaryius Thomas, LB Brandon Marshall and CB Bradley Roby.
Joseph says general manager John Elway hasn't conveyed any trade talks to him, and "that makes it rumor. That makes it gossip. And that makes it right now something that we can't worry about."
DENVER DISTRACTIONS: Besides the trade talk, the Broncos dealt with the drama of backup quarterback Chad Kelly's dismissal following his arrest on suspicion of criminal trespass.
"We have a great locker room. We have a close-knit football team and their focus is the Chiefs," Joseph said. "They all feel bad for Chad. They will support Chad as their former teammate. But we have one focus and that's the Chiefs on Sunday morning."
CHUGGING CHUBB: One of the reasons Mahomes was able to escape the pocket and do damage on the run in the first matchup with Denver was that rookie linebacker Bradley Chubb had trouble setting the right edge on defense. But he's hit his stride with five sacks in his last two games.
"We've got to be able to finish strong," Chubb said.
O-LINE TURNOVER: The Chiefs are poised to have another starting offensive line combination after losing C Jordan Devey to a torn pectoral muscle. He was already playing in place of Mitch Morse, who remained out with a concussion. Right guard Laurent Duvernay-Tardif is also out with a broken leg, all of which means recently signed offensive lineman Jeff Allen could start against Denver.
"We'll just see how that goes," Chiefs coach Andy Reid said. "We'll see how it rolls."
MORE FROM MAHOMES: This will be the eighth NFL start for Mahomes and already his third against the Broncos. He made his NFL debut against them in Week 17 last season.
"I mean, you get a little more familiar with a defense whenever you play them a lot, especially playing them this last game. They threw a ton at me, a ton of different blitzes and looks," he said. "It's something that I'm going to be able to take into this next game."