Rooney, the 32-year-old Englishman, had scored once and assisted on two goals by Acosta, a 24-year-old Argentine. Their sterling performances, combined with Bill Hamid’s breathtaking saves and the team’s disciplined effort against MLS’s most lethal attack, propelled United up another spot in the Eastern Conference and back within striking distance for a playoff spot.

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D.C. (8-11-6) passed New England for seventh place and crept within six points of the last postseason berth, held by Montreal, which has played three additional matches.

“It was a massive result for us,” Rooney said. “With Montreal winning [Saturday], we knew it was not a must win, but it felt like it.”

D.C. derailed Atlanta’s seven-game unbeaten streak and ended league leader Josef Martinez’s scoring run at nine matches.

The Acosta-Rooney partnership continues to grow since the former Manchester United superstar arrived in early July. It has been particularly beneficial to Acosta, who has posted six goals and three assists in the past eight matches after recording one goal in the first 19 games.

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Rooney raised his totals to four goals and five assists in 11 outings.

“Since the second [Rooney] got here, they created a very good bond on the field,” Coach Ben Olsen said. “Those guys find each other. It’s been fun to watch them.”

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Defensively, D.C. conceded a goal on a set piece and allowed Atlanta to enjoy 62 percent of possession but disrupted the high-powered attack in the run of play.

“We figured out the moments we needed to defend,” Acosta said, “and attack in the moments we needed to attack.”

The defensive effort received a boost from Paul Arriola, an attacker thrust into the right-back slot in place of injured Oniel Fisher.

As it often does, Atlanta (16-5-6) set the terms, but D.C. withstood pressure and, as the match evolved, seized on the prime moments to attack.

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Against the run of play, D.C. went ahead in the 29th minute. Hamid delivered a long ball. Rooney won the header, nodding the ball ahead to Acosta, who had slipped behind Jeff Larentowicz. Off he went, dribbling into the penalty area, pulling the ball back from Larentowicz and Leandro Gonzalez Pierez and slotting a 12-yard shot.

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Hamid thwarted Miguel Almiron, but D.C.’s lead was gone by the 39th minute as Larentowicz beat Rooney on Ezequiel Barco’s corner kick and placed a six-yard header into the far corner.

D.C. reclaimed the lead seven minutes after intermission on a sequence created and finished by Rooney. A terrific through ball met Arriola in stride behind the defense. As Arriola maneuvered in the box, Barco clipped his heel, prompting referee Allen Chapman to award a penalty kick. Rooney converted, his first goal in four matches.

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Atlanta was a constant threat. Hamid stopped Hector Villalba’s near-side bid and, on the end of Almiron’s 50-yard run, Martinez missed wide.

Counters against an increasingly desperate foe allowed D.C. to finish it. After Rooney faltered in the open field, Acosta all but secured the three points. Rooney was the provider, liberating the little Argentine, who worked Larentowicz and beat Guzan with a low shot from 15 yards.

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“It’s fun to watch and fun to be on their team,” Arriola said of Rooney and Acosta. “That’s what happens when you get two players who are of great quality and understand each other well. They don’t speak the same language, but I’ve always said on the soccer field the only language you need is the ball and the understanding on the game.”

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Hamid extinguished Atlanta’s comeback hopes with a breathtaking save on Kevin Kratz’s 30-yard free kick and reflex stop on Larentowicz’s close-in header.

D.C.’s path does not get any easier. International call-ups will cost United four regulars — Arriola, Junior Moreno, Darren Mattocks and Zoltan Stieber — for Saturday’s visit to third-place New York City FC, which is unbeaten at home. (NYC will miss three starters.)

“We held the fort,” Olsen said. “Now we need to build on this and go up to New York and get more because we still have a long way to go.”