In the second half, D.C. United's Chris Pontius fends off Philadelphia's Keon Daniel at RFK Stadium. (Katherine Frey/THE WASHINGTON POST)

D.C. United began the day in a troublesome spot, stuck at the bottom of MLS’s Eastern Conference standings and showing scant signs of being able to resuscitate a disconcerting season.

So how did United respond Sunday? By conceding two goals in the first 11 minutes, the gateway to a 3-2 defeat to the Philadelphia Union in front of 12,349 at RFK Stadium.

“The way we started the game is just unacceptable,” said Coach Ben Olsen, whose squad lost its third straight at home and fourth in a row overall to fall to 1-5-1. “It’s very alarming the way we started in the situation we are in.”

It wasn’t as if the Union scored a set of dazzling goals. When all else has failed this spring, Olsen could rely on his defense. Not this time.

Center backs Dejan Jakovic and Brandon McDonald mangled the first threat. A long ball and cross led to the second goal. And after United halved the deficit, Philadelphia (3-2-2) scored off a throw-in in the 26th minute.

Lionard Pajoy’s header early in the second half pulled United within one again, but an attack that has produced just four goals this year failed to capitalize on sustained possession.

“I truly am very frustrated right now,” captain Dwayne De Rosario said. Given the fragility of United’s situation, De Rosario chose his words carefully and said no one is ready to give up on a season with 27 games remaining. But he also said United went about things incorrectly in seeking a late equalizer.

“Ten minutes left, we start lumping the ball” upfield, he said. “We have guys who can play. There is no need for that. We are playing into our weaknesses instead of our strengths. And it’s a big problem right now.”

The problems began in the seventh minute. Philadelphia’s Brian Carroll blocked Jakovic’s pass in midfield, allowing Conor Casey to quickly pick out Jack McInerney straddling the offside threshold.

McInerney accelerated. Jakovic and McDonald closed but, in a comical and inept attempt, let him slip between them. McInerney skipped into the clear for a 15-yard shot past Bill Hamid.

Four minutes later, Sheanon Williams sent a long ball to Danny Cruz, who cut back on Daniel Woolard on the right side and crossed to Casey in a pocket of space at the top of the box. Casey’s low drive zipped between the sliding Jakovic’s legs. Hamid got his left hand on it but couldn’t stop it.

“We did everything wrong,” midfielder Marcelo Saragosa said of United allowing the early goals.

United answered in the 17th minute on Perry Kitchen’s second career goal. McDonald’s incisive pass from beyond the box connected with De Rosario, who one-timed a pass back to the oncoming Kitchen for a 12-yard shot past Zac MacMath, ending the club’s 265-minute scoreless streak.

But another breakdown in the 26th minute allowed the Union to regain a two-goal edge. This time, United failed to properly defend a throw-in. From the heart of the box, Amobi Okugo flicked Williams’s long toss to the back side, where McInerney settled the ball and finished with composure for his sixth goal of the season.

McInerney, 20, was the seventh selection in the 2010 MLS draft — a slot Philadelphia acquired from United in what turned out to be a one-sided trade: The Union added McInerney, veteran midfielder Fred and financial considerations for goalkeeper Troy Perkins, who lasted one season in his second stint in Washington.

United did not go quietly. Three minutes into the second half, Pajoy headed in Woolard’s cross from six yards for his second goal of the year. But MacMath was not forced to make a difficult save the last 40-plus minutes.

“Everybody is worried about what is going on right now,” forward Carlos Ruiz said. “This is one of those moments in soccer where you cannot find the way to win. But it’s going to come. It has to come, sooner or later.”

United notes: Marcos Sanchez, who started the previous two matches, was not available because of a sprained ankle – the fourth midfielder sidelined with an injury.