ORLANDO — With six teams packed tightly behind the two pacesetters in MLS’s Eastern Conference, the slightest misstep or missed opportunity, one bad night or empty performance, promises to prove costly in the playoff scramble.

D.C. United began the weekend in third place but just three points from eighth, a fragile affair as Hernán Losada’s surging bunch arrived in Central Florida for a showdown with another side seeking breathing room above the seven-team postseason threshold.

Just as United was about to escape with a valuable away point, the visitors conceded Daryl Dike’s header in the seventh minute of stoppage time and dropped a 2-1 decision to Orlando City before an announced 16,848 at Exploria Stadium.

In a frantic closing scramble, Chris Mueller served a corner kick. Dike, the former University of Virginia star, was marked by a smaller player, Russell Canouse. Donovan Pines was late to help, and Dike sent a glancing header off the underside of the crossbar for his sixth goal of the season.

Once a D.C. strength, set pieces have become a liability. The past three conceded goals have come on a free kick or corner kick.

“We were very strong at the start of the season, and now there is kind of a weakness,” Losada said. “Of course, you can defend better than that, but the corner is perfectly given.”

Orlando never should have gotten the opportunity, D.C. captain Steven Birnbaum said, claiming the ball was knocked out by an Orlando player. TV replays supported his argument.

“That’s frustrating, to say the least,” Birnbaum said. On the goal, Dike “made a good run, and we’ve got to get there first. … We were pretty stout defensively [overall], so it was just unfortunate to give up a set piece like that.”

Julian Gressel continued his torrid stretch with an early goal for United (12-12-4), which relinquished third place to Orlando (11-8-9) and fell even with Montreal (11-10-7) on points (40) for fourth but remained ahead in the tiebreaker. Each of those teams has six games left. Three teams have 39 points.

Robin Jansson scored in the 17th minute for Orlando, which was winless in its previous five matches.

United was as forward-thinking here as at home, eager to set the terms against a wobbling opponent. It took until only the sixth minute to seize the lead.

Birnbaum won a header in midfield, and following a connection between Júnior Moreno and Paul Arriola, Canouse one-timed the ball wide to Gressel overlapping on the right flank.

With time and a pocket of space, Gressel ripped a 25-yard rocket that beat Pedro Gallese to the near corner for his second goal in two matches. (He also has five assists in the past five games.)

The advantage did not last long. After Birnbaum toe-poked a cross to prevent a tap-in by Dike, Orlando scored on the ensuing corner kick.

Bill Hamid stopped Júnior Urso’s header but left the rebound for the unmarked Jansson to bash into the roof of the net from close range.

Orlando continued to grow into the game, circulating the ball and delivering teasing deliveries into the penalty area.

Already with one yellow card, D.C. defender Tony Alfaro was in danger of a second with risky challenges. Losada did not take any chances, replacing him with Joseph Mora late in the half.

Another change was necessary at halftime after Yordy Reyna hurt his right leg just before intermission, a setback that could undermine his plans to join the Peruvian national team Sunday for World Cup qualifiers.

Edison Flores, a fellow Peruvian, entered. Fifteen minutes passed when, with Arriola cramping, Losada turned to a second natural striker, Nigel Robertha, to join MLS leading scorer Ola Kamara.

The onus to win was on the home side, but United continued to push. Robertha was heavily involved on the right side partnering with Gressel, and Flores brought fresh legs and ideas.

It reached the point, though, when Losada needed to secure the draw. He exhausted his five substitutions in the 82nd minute, adding defensive reinforcement (Felipe Martins and Chris Odoi-Atsem) at the expense of attackers (Kamara and Gressel).

Orlando threatened in the 88th minute when Dike powered into the box and touched the ball to Tesho Akindele. Hamid, though, made a sprawling save, and Mora cleared the rebound from danger.

An initial six minutes of stoppage time, then a seventh and eighth, brought additional tension and two last-gasp corner kicks, the second resulting in Dike’s winning header and bedlam in the purple-laced stadium.

It was a gutting blow to United entering a two-week break for the international window.

“Unfortunately,” Losada said, “two set pieces ended up making the difference.”

Notes: Kevin Paredes, the electrifying left wing back, traveled but was not in uniform with what team officials described as a minor injury. Odoi-Atsem (quadriceps) was in uniform for the first time since Aug. 21. …

Besides Reyna, Arriola (United States), Andy Najar (Honduras), Moreno (Venezuela) and Flores (Peru) are also scheduled to report to their respective national teams for a stretch of World Cup qualifiers. …

United is off until Oct. 16 at home against second-place Nashville.

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