Flacco went 25-of-34 through the air for 265 yards with no interceptions, connecting with Ray Rice for a go-ahead, 9-yard scoring strike in the second quarter and finding Anquan Boldin on a 4-yarder in the third that made it 23-7 Baltimore.
Willis McGahee added a 25-yard touchdown run and Billy Cundiff kicked three field goals for the Ravens, who forced five Kansas City turnovers and now advance to face Pittsburgh Saturday.
The Chiefs, meanwhile, were limited to 161 yards of total offense as quarterback Matt Cassel completed just 9-of-18 passes for 70 yards and three interceptions.
Jamaal Charles scored the only points for the AFC West champs on a 41-yard touchdown run in the first quarter.
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