It was the worst regular season loss for San Francisco, already winners of the NFC Western Division title, since a 59-14 defeat at Dallas in 1980. San Francisco also suffered a 49-3 play-off defeat to the New York Giants in 1986.
"We played as well today as I think we can play," Marty Schottenheimer, the Chiefs' coach, said. "There's clearly not that kind of point differential between us. It was just one of those days. Things went our way."
"The wheels came off a bit and then it snowballed," Steve Mariucci, the 49ers coach, said. "We got frustrated."
Gannon, making his fourth start for the injured Elvis Grbac, completed 12-of-21 passes for 186 yards. He has led the Chiefs to consecutive victories over Denver, Seattle and San Francisco. Kansas City remained one game behind Denver, leaders of the AFC West.
Rison caught five passes for 117 yards, including touchdowns of six and 29 yards. Gannon also hit the rookie tight end Tony Gonzalez with a two-yard scoring pass. Marcus Allen scored on a three-yard run and connected with the tight end Ted Popson, a former 49er, on a one-yard touchdown in a 21-point second quarter for Kansas City.
Meanwhile, in San Diego, John Elway threw for 240 yards and three touchdowns and Terrell Davis ran for 178 and a score in his homecoming as the Denver Broncos became the first AFC team to earn a play-off place with a 38-28 victory over the Chargers.