Smith and Davis combined on a 21-yard scoring strike to open the scoring in the first quarter and capped San Francisco's output with a 23-yard TD late in the final period.
Smith finished 20-of-31 through the air 226 yards and wasn't picked off, while Davis made five grabs for 75 yards.
Gore racked up 89 yards on 17 carries.
Jason Hanson kicked four field goals for the Lions (1-1).
Detroit signal-caller Matthew Stafford completed 19-of-32 passes for 230 yards with one fourth-quarter TD and one interception.