Aiming to keep their playoff hopes alive, United (6-12-4, 22 points) also ended an 0-4-2 rut with an early offensive surge that proved to be enough to earn their first taste of victory since Oct. 3.
Cincinnati (4-14-4, 16 points), owner of the fewest points in MLS, was eliminated from playoff contention after losing its fourth in a row and eighth in its last nine.
Playing with a sense of urgency and looking for a strong start, Atlanta came through just eight minutes into the match.
Following some stellar one-on-one footwork against FC Cincinnati defender Andrew Gutman, Jurgen Damm delivered a perfect pass across the box to a waiting Jahn, who easily drilled the ball into the right corner of the net for his third goal of the season.
The hosts made it 2-0 in the 26th minute, this time via a penalty kick from Moreno. United was set up from the spot after Jon Gallagher was tripped in the box by star Cincinnati defender Kendall Waston. Moreno then drove the ball right down the middle for his first MLS goal.
Cincinnati made some noise late in the first half. The visitors got a pair of quality, up-close strikes, but Atlanta keeper Brad Guzan slapped both attempts away.
Cincinnati was blanked for a third consecutive match, but actually held a majority of the possession in the second half. It took 14 shots overall and put four of those on target, but was unable to test Guzan any more than it did in the first half.
FC Cincinnati's 11 goals in 2020 are by far the fewest in the league. They have also failed to score in four consecutive road contests.