LAS VEGAS — After Derek Carr led the Raiders to the brink of another victory over the defending Super Bowl champions, Las Vegas coach Jon Gruden described his quarterback as “almost flawless.” That’s almost good enough to beat Patrick Mahomes and the Kansas City Chiefs, but not quite. Carr went 23 of 31 for 275 yards and three touchdowns with a 119.7 passer rating Sunday night, but Mahomes matched Carr’s two scoring drives in the fourth quarter with two of his own.