David Montgomery scored on a 3-yard run on third-and-two, giving the Lions a 10-7 lead with 4:34 left in the third quarter.
The Lions last led at 3-0 at the 10:46 mark of the first quarter.
The Cowboys received the second half kickoff but couldn’t do anything with it. Tyron Smith had a false start, and the Cowboys gained only 14 yards and picked up one first down before punting.
Detroit went 74 yards in 13 plays, converting a fourth-and-two from the Dallas 41 on a 4-yard thrown from Jared Goff to rookie Sam LaPorta.
Goff is 10-of-18 for 105 yards with an interception, and Montgomery has 13 carries for 64 yards.