Even with the Broncos' overtime win over the Bengals Monday night, Denver's lead in the AFC West is not safe. Should they lose to the Chargers in the season finale and the Chiefs beat the Raiders, the Chiefs would steal the AFC West crown right off of their heads.
A major reason the Broncos are in danger of losing the AFC West right now is because the Raiders beat them two weeks ago. So, essentially the Raiders made it so both the Broncos and the Chiefs would be fighting for the division crown.
Currently they sit in the 5 seed spot where they will face the winner in the AFC North (most likely the Texans). There is no scenario in which the Chiefs could get a first round bye, but winning the division would move them to the 3 seed and give them home field in the wildcard round. While a loss could drop the Chiefs to the 6th seed where they would either head to Denver or Cincinnati in the wild card round.
Last season the Raiders helped keep the Chiefs out of the playoffs. Even with the Raiders much better record this season (7-8) than last year's 3-13 finish, they are still playing for pride this week. And even with the Chiefs already in the playoffs, they haven't WON a playoff game in 22 years -- a string of 7-straight playoff opening losses. Winning the division and/or securing home field advantage in the opening round is very important to trying to end that streak. The Raiders stand in the way of that.