DENVER (AP) - The Kansas City Chiefs are the NFL's worst undefeated team.
Peyton Manning is the league's most vulnerable 300-yards-a-game passer.
It's not often that so many doubts hover over teams and players who have been so good.
Some of the questions will be resolved Sunday night when the Chiefs (9-0) play the Broncos (8-1) in an AFC West meeting between teams with a .944 winning percentage - best combined record of two opponents this deep into the season since the NFL merger in 1970.
But not all the questions. Because they meet again in two weeks.
''The NFL has a system in place to find out who's the best,'' said Chiefs quarterback Alex Smith, who has fielded repeated questions about the softness of Kansas City's schedule through nine games. ''The speculation of nine weeks in, who's the best team, for me, it's kind of pointless. Who cares? I want to be the best team come February.''
A win for Kansas City would go a long way toward that goal. The Chiefs, whose nine straight victories have come against teams with a combined .357 winning percentage, could take a two-game lead over the Broncos with an early edge in the tiebreaker and a rematch coming up Dec. 1 at home.
If the Broncos win, they'll move into a tie in the AFC West with the toughest stretch of their season - at New England and Kansas City - coming up next.
The buzz about Manning's record-pace of 3,249 yards and 33 touchdowns this season has been replaced this week by concerns over his ankles. They have been bugging him for about a month now and got worse when a Chargers lineman dived at them at the end of last week's game.
The Broncos get ready to protect him while facing the league's top sacks defense; linebackers Justin Houston (11) and Tamba Hali (9) have combined for 20 of Kansas City's 36 sacks. The Chiefs also lead the league with a plus-15 turnover margin.
In a matchup between top offense and top defense, who usually wins?
''Well, the NFL definitely made it harder for a really good defense in this league, but you have to play the game to find that out,'' Broncos cornerback Champ Bailey said. ''It could go either way. We know what kind of defense they have and we know what kind of offense we have.''
Five things to look for Sunday in ''The Game of the Year, Part I:''
PEYTON'S ANKLES: An MRI showed no new damage to Manning's ankle after last week and Manning has been saying all along he'll play. Still, it's hard to put a measure on the week-after-week toll of having players diving at his feet, let alone sacking and stripping him from the blind side, which has happened in the last three games. ''It's part of football,'' Manning insists. Clearly, though, this is not the perfect week to be going up against the league's top sacks team.
KC KEEPING UP: The Chiefs' defense has scored five touchdowns this season. The offense: four TDs over the last three games. The Broncos average 41.2 points a game. Even if the Kansas City defense keeps Manning and Co., in partial check, and even if the defense scores a few points itself, it figures there will be at least some pressure on Smith and the KC offense to score a bit. The Chiefs rank 26th on converting trips inside the 20 into touchdowns (82.8 percent). ''You want sevens, and when you get them, the chances of winning go up,'' Smith said.
BRRRR: Temperatures are forecast to be in the 30s for kickoff, which means Manning could very well don his cold-weather glove for the first time this season. The last time he wore it in a meaningful situation, the Broncos lost to Baltimore in the playoffs in single-digit weather. The time before that, they beat Kansas City 38-3 in the 2012 regular-season finale.
Either way, Manning is far less effective when the weather is cold - 8-10 lifetime when the temperature is 40 or below - and the surgeries he's had on his neck have caused some nerve degeneration that make it harder for him to grip the football when the temperature drops.
DISTRACTION BOWL: The Broncos adjusted well with Jack Del Rio taking over for John Fox while Fox rests at home following heart surgery. This week, the glare of the distractions goes to Kansas City's side, where receiver Dwayne Bowe was arrested last weekend during the team's bye and charged with speeding and possession of marijuana. Coach Andy Reid has said virtually nothing, other than that his star receiver would play and start. The Chiefs need him. Hard to match the Broncos point for point without the man who has caught more passes (33) for more yards (369) than any Kansas City wideout.
RUNNING BACKS: If the Chiefs are going to win, it would figure Jamaal Charles will have a(nother) big game. He leads the Chiefs in both yards rushing (725) and receiving (389). Yet, strange as it sounds for a team led by Manning, Broncos running back Knowshon Moreno could have every bit as big an impact for the Denver offense.
Moreno kept his starting job this season because he's best at protecting Manning. As Manning's protection has faltered a bit and teams have pressed the Denver receivers, Moreno has turned into his quarterback's favorite target: He leads the team in receptions over the last four games, with 24.
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