Devin Smith had not caught a pass since 2016. His first catch in 2019 went for a touchdown.
The Cowboys receiver beat Josh Norman for a 51-yard touchdown pass from Dak Prescott with 6:10 remaining in the first half.
It tied the game at 7-7.
Smith entered the game with 10 career catches for 135 yards and a touchdown, all with the Jets, who made him a second-round pick in 2015.
The Cowboys have 144 yards and Washington 92 in a defensive battle.