The 27-year-old American was also making his first start for the club since September 2016, as he attempts to work his way back into the picture after a long period in the wilderness.
Johannsson was played through by Max Kruse in the seventh minute of the contest, and the U.S. international calmly chipped the ball over Bernd Leno in the Leverkusen net.
After suffering through injuries in previous seasons, Johannsson has found playing time hard to come by in 2017-18, making just six total appearances for the club this season.
The striker has begun to work his way into more playing time, however, grabbing a vital assist off the bench in last weekend's 2-1 win over Schalke.
That possibility was made less likely, though, when the 27-year-old was taken off at halftime with an injury against Leverkusen, with his side leading 2-1.
Bremen could certainly use Johannsson rounding back into form, with the club currently 15th in the 18-team Bundesliga table and facing a fight to avoid the drop this season.