DC United (9-12-6) ended a four-match losing streak in all competitions and snapped a three-match scoreless run against the Fire (8-11-8). The two clubs played to a scoreless draw earlier this season.
Benteke staked DC United to an early lead, using an assist from Mateusz Klich in the 9th minute to score his ninth goal of the season.
Benteke picked up an assist on Theodore Ku-DiPietro's fifth goal this season, giving DC United a 2-0 advantage in the 20th minute. It was 3-0 at halftime after an own-goal by Chicago defender Carlos Terán in the 41st minute.
Benteke hit double figures this season with his goal in the first minute of stoppage time to complete the scoring. Chris Durkin had an assist.
Alex Bono totaled three saves to earn a clean sheet in his second start and third appearance for DC United. Chris Brady saved one shot for the Fire.
DC United will host the San Jose Earthquakes on Saturday. Chicago returns to action on Sept. 16 when they travel to play CF Montreal.