Damon Huard completed 10 of 15 passes for three touchdowns and 148 yards. Tony Gonzalez caught five passes for 63 yards and two touchdowns, and Kris Wilson caught a touchdown pass for the Chiefs (5-3), who have built a three-game winning streak.
Courtesy of two scoring passes by Huard, the Chiefs led 24-10 at the half.
For the Rams (4-4), Marc Bulger went 31-for-42 for 354 yards and one touchdown. Steven Jackson rushed for 86 yards on 19 carries and caught 13 passes for 133 yards, and Kevin Curtis caught seven passes for 59 yards and a touchdown.
Johnson's touchdown following a St. Louis turnover gave the Chiefs a 7-0 lead in the first quarter.