They traded for under-used speedy Jamaican striker, Darren Mattocks and acquired another Costa Rican, midfielder Ulises Segura.
Twelve of the first fourteen games were on the road, as the team awaited the completion and opening of their new Buzzard Point stadium, to be called Audi Field.
The intimate setting and snowy weather made for a unique experience, but the team continued its struggles, surrendering two first-half goals.
United handed the visitors a man advantage when Paul Arriola was shown a red card early in the second half.
The long road trip resumed, and so did the losing, with a pair of 3–2 defeats at the hands of Philadelphia Union and Real Salt Lake.
The team seemed to be showing progress and earned a 1–1 draw in their first trip to Los Angeles to face potent expansion side LAFC.
The road trip ended with yet another 3–2 loss, to New England Revolution and yet another draw in Los Angeles, this time a 2–2 affair against LA Galaxy.
However, a giveaway in stoppage time led to a goal by Vancouver's teenage sensation Alphonso Davies, spoiling Ousted's bid for his first clean sheet of the season.
New York Red Bulls spoiled the second match at Audi Field, as Bradley Wright-Phillips put the visitors on top with a second-minute goal, a lead they never surrendered, despite an uncalled penalty shout for Rooney in the second half.
Deep in stoppage time, United lined up a corner kick and goalkeeper Ousted pushed forward to try to get the winning goal, to break the 2–2 tie.
Rooney then rose and dribbled back in the opposite direction before a sending a long pass across the field, into the box, where Acosta was able to head it for the winning goal at the death.
Hamid's return was marked by a pair of solid wins, 4–1 over Portland Timbers on the strength of a brace by Rooney that included his first free kick goal, and a 2–0 over New England.
The 3–3 draw temporarily left D.C. United 4 points off the pace for the final playoff spot, but with a game in hand over Montreal Impact, whom they would play in their next home match, to close out September.
A sell-out crowd watched D.C. United host the Montreal Impact in a crucial match in the race or the final playoff spot in the Eastern Conference.
In the 78th minute D.C. stretched its lead to 4–0 as Arriola beat the goalie to a loose ball and scored his second of the match, and giving Acosta his 3rd assist.
The final month of the regular season, October, opened with Montreal posting a 3–0 win over Columbus and Philadelphia an even bigger winner over Minnesota.
Hosting Chicago Fire, D.C got off to a good start but squandered several chances in the first half, including an apparent Rooney goal, waved off for a foul after a video review.
In a midweek match against the defending champions, Toronto F.C., United did the deed early on when Wayne Rooney scored a memorable goal on a 40-yard free kick that curled back just inside the post.
D.C. United clinched their place in the 2018 MLS Cup Playoffs in style, rounding out their 2018 home regular season campaign with a convincing win over visiting NYCFC, extending the team's unbeaten streak to nine games.
The first came when Acosta went on a run from the sideline maneuvering through several defenders before cutting the ball to Rooney for a simple tap-in at the top of the six-yard box.
D.C. was unable to score against Chicago Fire, but a 0–0 was enough to put D.C. ahead of Philadelphia into 4th place, and earned a home game in the one-game opening playoff round, against the Columbus Crew.
Playing in front of one of the most raucous home crowds in team history, D.C. United took a 1–0 lead in the first half, when Brillant pounced on a loose ball in the box, heading it for a goal after a misplay by the Columbus Crew goalie Zack Steffen.
Shooting in the fifth spot, DeLeon put his shot over the crossbar, giving the Crew a 3–2 winning margin in the shootout, ending D.C. United's season.