Running back Damien Williams rushed for 124 yards and two touchdowns on just 12 carries Sunday as the Kansas City Chiefs won their sixth straight, downing the Los Angeles Chargers 31-21 at Kansas City, Mo.The Chiefs (12-4), who also relied on 174 yards passing from quarterback Patrick Mahomes, head to the AFC playoffs with a first-round bye as the No. 2 seed after Miami upset New England 27-24 and dropped the Patriots to the No. 3 seed.On three of just five touches by the Chiefs in the third quarter, Mahomes threw an interception that the Chargers (5-11) converted into a touchdown, Mecole Hardman returned a kickoff 104 yards for a touchdown, and Williams scored on an 84-yard rush.The frantic exchanges left Kansas City with a 24-14 lead.Los Angeles quarterback Philip Rivers responded by engineering an 86-yard drive capped with an 8-yard touchdown pass to tight end Hunter Henry.That made it 24-21 with 5:23 left, but Kansas City answered with a 77-yard march that Williams finished with a 7-yard scoring burst. The Chiefs swept their AFC West opponents and have won 28 of their last 31 against division rivals.The 224th consecutive start for Rivers could have been the veteran quarterback’s last game for Los Angeles. He becomes an unrestricted free agent in March, after going 31 of 46 for 281 yards, two touchdowns and two interceptions.