CHESTER, Pa. — Over the course of 90 long minutes Saturday, Ben Olsen’s one-win MLS team labored to keep pace with another one-win team. That D.C. United was level after Darren Mattocks’s terrific equalizer with about 20 minutes left was testament to the wonders of a sudden goal and to the Philadelphia Union’s inefficiency.

But salvation lasted a mere 98 seconds, and with another defensive lapse, United conceded the go-ahead goal and dropped a 3-2 decision at a sun-splashed stadium on the banks of the Delaware River.

“What happens is you become passive,” Olsen said in describing the gap between reward and punishment. “We’re off a little bit and maybe too passive.”

United’s performance in general was too passive, and with it came dire consequences: a 1-4-2 record heading into weeks of heavy travel before its new venue, Audi Field, opens in mid-July.

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Zoltan Stieber scored early, and, moments after entering, Mattocks struck in the 70th minute for a 2-2 tie. But Borek Dockal took advantage of United’s inability to clear the ball in the 72nd as the Union (2-3-2) defeated D.C. here for the fifth consecutive time.

Philadelphia had scored one goal in the previous five games, but against United it enjoyed 61 percent of the possession and massive advantages in shots (23-4) and corner kicks (12-1).

“We can’t get in the habit,” defender Steve Birnbaum said, “of defending in our box for the majority of the game.”

Inevitably, United cracked, leaving Olsen and the players to explain another sour result. Since last fall, D.C. has won once in 11 outings.

Olsen said he is “not too alarmed.”

“It doesn’t feel good, and I don’t think we played up to our capabilities. So that’s concerning,” he said. “But I’m not concerned about our ability to win games. The group will be fine.”

It wasn’t against one of the weakest teams in the 23-strong league.

“It would’ve been a good result for us if we could at least take one point from here,” Stieber said. “It’s quite disappointing.”

It started well enough. Two weeks after striking in the first minute against Columbus, United needed seven minutes Saturday.

Ulises Segura blocked Jack Elliott’s pass out of the back and directed the ball to Yamil Asad for a one-touch to Luciano Acosta. The Argentine slotted a through ball to the free-running Stieber for a one-touch finish from 12 yards. Stieber’s first goal of the year ended a four-game scoreless streak for United in Chester.

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Philadelphia squandered several promising buildups before equalizing in the 37th minute. Ilsinho beat Joseph Mora on the right side of the penalty area and directed a low ball to the six-yard box. He was targeting C.J. Sapong, but the offering clipped defender Frederic Brillant’s right ankle and caromed past goalkeeper Steve Clark.

It initially ruled an own goal, but Ilsinho was later credited.

Four weeks ago, Brillant’s early deflection of Felipe Gutierrez’s bid provided Kansas City with a 1-0 victory.

Intermission failed to interrupt the Union’s flow. With United pinned into its own end, another goal was certain.

And in the 60th minute, with United’s resistance bending, Haris Medunjanin lifted a pass to Alejandro Bedoya deep on the right side of the penalty area for a header across the six-yard box to Sapong. The Manassas native nodded a downward header into the left side of the net.

Against the grain, United pulled even in the 70th when Mattocks met Stieber’s wonderful long cross with a running, leaping seven-yard volley.

D.C.’s fortunes turned again, however. Unable to alleviate danger with a simple clearance, United watched Dockal turn and smash an angled nine-yarder over Clark and into the roof of the net.

“It’s definitely a bit frustrating, but it’s still a long season,” defender Nick DeLeon said. “We’re in a tough stretch right now and have a lot of home games to come. We’ve got to keep the team together and move in the right direction.”

So far this season, the only directions have been sideways and backward.

United notes: Brillant, a native of France, received U.S. permanent residency and no longer counts against the international player limit, freeing a slot for future moves. …

With the first transfer and trade window closing Tuesday, General Manager Dave Kasper said: “There’s been some recent inquiries about various trades. At this point, it’s unlikely we make a move. We’ll see what Monday-Tuesday brings.”

The summer window (July 10-Aug. 8) offers greater opportunity to sign players from abroad. …

United is off next weekend and will visit Real Salt Lake on May 12.

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