December 28th, 2002. The Raiders beat the Kansas City Chiefs 24-0 in Oakland, only to go on to the Superbowl, but fell on their face 48-21 against former head coach Jon Gruden to start their 24-78 nosedive.
The Raiders overall record facing KC since 2001 is 5-14. Three of those wins have come in the past three seasons. And all three wins were at Arrowhead Stadium. Before that they were win-less at Arrowhead for five seasons dating back to September 9th, 2001.
The Chargers may be the most recent Raider nemesis with their 13 straight wins over them (tied for the longest streak in football for one team over another), but at one time the Chiefs had the Raiders' number as well. And the Raiders haven't swept the Chiefs in a season for nine years.