Wayne Rooney, right, had no magic Wednesday night against Philadelphia Union midfielder Alejandro Bedoya. Philadelphia earned a 2-0 win at Audi Field. (Brad Mills-USA TODAY Sports)

Over three crackling weeks, D.C. United had revived its MLS postseason hopes by playing stylish soccer at its new stadium and compiling a long-awaited string of victories while looking ahead to a home-heavy remaining schedule.

But after a second defeat in 72 hours Wednesday — plus the prospects of tired legs chasing the league’s most potent team this weekend — United’s outlook has dimmed and its margin of error has narrowed.

A 2-0 defeat to the surging Philadelphia Union before an announced 17,692 at Audi Field left Ben Olsen’s side stuck in eighth place entering the final eight weeks of the campaign. United (7-11-6) has still played fewer games than the rest of the Eastern Conference, but empty performances, particularly at home, are not helping the cause of getting into the top six.

“We just lacked quality, and a lot of that is fatigue,” Olsen said. “We got in good spots and just didn’t have that extra bit of power. It was just kind of stagnant.”

While United labored, C.J. Sapong, a Northern Virginia native, scored in the first half and Fafa Picault struck 15 minutes after intermission to end United’s home winning streak at four. After scoring nine goals in a three-game span, D.C. has gone scoreless in the past two outings and must now prepare for a visit by MLS Cup favorite Atlanta United on Sunday.

“No excuses,” forward Wayne Rooney said. “They were the better team.”

United labored in trying to replicate the artful rhythm that had helped revive the season. Aside from Luciano Acosta’s moments of brilliance — and the fleeting menace of Acosta’s partnership with Rooney — D.C.’s passing was off, its movement a bit slow and its decision-making suspect in the final third of the field.

“It’s not a question,” midfielder Paul Arriola said. “We were tired.”

United was back at it after playing away Sunday night against the New York Red Bulls. A game-time temperature of 89 — it felt like 101 — compounded the physical challenge.

Olsen did not hold back with his lineup choices — the lone absence was injured attacker Yamil Asad — as he saw greater opportunity to earn three points against Philadelphia (12-11-3) than against Atlanta, the highest-scoring team in the league.

However, Olsen said, “when we concede the first goal, it’s going to be a long night because now you have to chase the game. We’re coming off two days’ rest, it’s been a hot week, the Red Bulls game was a physical matchup that maybe took a little bit more out of us than I thought.

“You saw it in the second half: We’re cooked.”

Three days after Rooney hit the crossbar, his hard luck continued in the eighth minute with an 18-yard bid that clanked the near post. In the 22nd, benefiting from Acosta’s open-field brilliance, Rooney chipped the ball over goalkeeper Andre Blake but watched it drift wide of the far post.

Philadelphia, which has won four straight, broke through on a 29th-minute counterattack. Sapong set up Cory Burke for a low blast thwarted by goalkeeper Bill Hamid. Sapong — a graduate of Forest Park High in Prince William County and James Madison University — beat Russell Canouse to the rebound for a sliding finish.

United pleaded for a penalty just before intermission, but video assistant referee Mark Geiger did not deem Jack Elliott’s contact on Arriola’s touch worthy of review by referee Nima Saghafi.

“I don’t understand how it’s not checked” by Saghafi, Arriola said. “I’ve looked at the replay and I don’t understand it.”

Added Olsen: “It looks like a handball. If it doesn’t hit his hand, Paul is going by him, no? I think it’s one of those you can call or not call. That’s the world we live in.”

At the start of the second half, midfielder Ulises Segura replaced defender Oniel Fisher (hamstring), but Philadelphia doubled the lead in the 61st minute. Unmarked on the right side, Sapong crossed to the uncovered Picault for a one-timer past Hamid from 10 yards.

Olsen inserted forward Darren Mattocks for defensive midfielder Canouse, but then swapped central defenders instead of resting Rooney or Acosta for Sunday.

“No,” Olsen said, “that did not enter my mind to rest guys.”

United notes: Asad (bruised left ankle) listed as day to day and seems unlikely to start this weekend. . . . The team has finalized plans to host Honduran club Olimpia in a Sept. 19 friendly, part of an effort to introduce more Latin American fans to Audi Field and provide a semi-competitive match during a 13-day gap between league games. United is also slated to host the Salvadoran national team Oct. 3.

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