The Lions had their 25th rushing touchdown of the season when wide receiver Jameson Williams took an end around 3 yards for the score.
Detroit was within an extra point of tying the game, but Jordan Elliott blocked Jake Bates kick.
The 49ers lead 7-6.
The Lions had seven runs and two passes on their first drive with Jahmyr Gibbs carrying three times for 32 yards, including a 21-yarder, and Jemar Jefferson getting two carries for 6 yards.
It was Williams’ first rushing touchdown of the season.
Jared Goff went 2-for-2 for 29 yards, with Craig Reynolds catching one for 26.
