DENVER -- Forget about the rematch against the Denver Broncos in two weeks. There's only one game on the Kansas City Chiefs' schedule that matters now, and it's next Sunday's meeting with the San Diego Chargers at Arrowhead Stadium.

The Chiefs have to get their swagger back. They haven't played their game in several weeks, and on Sunday night they paid for it by losing for the first time this season, 27-17 to the Broncos.

It's just one game, and at 9-1 the Chiefs are still tied for first place with the Broncos in the AFC West. Still, their world suddenly feels like it's teetering. That's what happens when a defense that had carried the Chiefs through the first nine games collapsed, failing to make a single impact play in Denver's 76 offensive snaps.

Think about that for a second. The Chiefs, the league leader in sacks, never got to Peyton Manning, rarely even got a hand on him.

The Chiefs, the league leader in turnovers forced, got one takeaway, but it wasn't forced. A bad exchange on a handoff between Manning and Montee Ball wound up on the ground, and the Chiefs' Derrick Johnson was there to pick it up.

"That's us. That's what we do," Johnson said, referring to the sacks and turnovers that fueled the Chiefs through their 9-0 start. "It's just one game where we didn't do what we usually do."

Similarly, coach Andy Reid described the loss as just one bad day.

"We played a good football team," Reid said. "They got us today."

The Chiefs had better not fall into that trap. They haven't been themselves for weeks, and to believe the Chiefs will return to their previous form is, in all likelihood, wishful thinking.

The Chiefs didn't get a sack in their previous game against Buffalo, either. The week before that, they had just one against Cleveland.

Not every opponent will be able to exploit Kansas City's defense like the Broncos, who have Manning at quarterback and an impressive array of receivers. But other opponents have caught on to Kansas City's methods of pressure and have adjusted. The Chiefs need to adjust as well.

"It's one thing to say offenses are catching up to us just because we lost one game," cornerback Sean Smith. "Our defense is still very good. We're not hanging our heads low. You've got to give some credit to the offense. They're very efficient. They don't make too many mistakes. But still we have to find some kind of way to force turnovers. We definitely need more opportunities for our offense."

Perhaps the Chiefs will bounce back next week against the Chargers and return to their dominant form. Yet some ominous signs popped up against the Broncos that more likely mean it could be some time before the Chiefs right themselves defensively.

Rookie cornerback Marcus Cooper, who had been a gem since he was pulled off waivers from San Francisco to begin the regular season, had his worst game. Linebackers Justin Houston and Tamba Hali looked like average pass-rushers.

When opposing quarterbacks get rid of the ball quickly, as Manning mostly did and Buffalo's Jeff Tuel frequently did, the Chiefs look average, and sometimes not even that. So expect San Diego's Philip Rivers and other opposing quarterbacks to continue to throw quickly to neutralize Kansas City's pass rush.

"This league is a copycat league," Johnson said. "Whenever things work against you, other teams are going to do it, too."

Indeed, the fate of Kansas City's season depends on the defense pulling itself together. The Chiefs certainly can't count on their offense to carry them.

The Chiefs blew their only realistic chance to win Sunday night in the first quarter. After Johnson returned Manning's fumble to the Denver 18-yard line, the Chiefs had a chance to recover from an early 3-0 deficit.

Earlier in the season, they would have jumped all over the opportunity. This time, they returned the favor on the first play when fullback Anthony Sherman fumbled. Denver recovered and, with the help of a 70-yard pass from Manning to Demaryius Thomas, soon had a 10-0 lead.

It was Kansas City's first double-digit deficit of the season. Predictably, they couldn't overcome it.

So after just one defeat, the Chiefs' season has that fragile feel. They don't have much time to fix their problems. If they don't do it by next week's game against the Chargers, the Dec. 1 game against Denver might not matter much, anyway.

"We have a big division game coming up next week, so there's no time to feel sorry for ourselves," Smith said. "You take [the Denver loss] with a grain of salt."

They'll do so at their own peril.