Sebastian Miranda, right, of Columbus set up the winning goal against D.C. United in a 2-1 victory. (Jamie Sabau/GETTY IMAGES)

With every defensive malfunction that results in a deflating goal and blistering shot that clanks off the crossbar, D.C. United’s playoff aspirations take another hit during this exasperating season.

United remains very much in the race, but time — and games — are running out.

The latest setback came Sunday afternoon, a 2-1 defeat to the slumping Columbus Crew before an announced audience of 15,566.

United (9-10-11, 38 points) missed a chance to pull even with the Crew (12-12-8, 44), which was in an 0-5-1 rut.

D.C. defender Daniel Woolard scored for the first time in three years, but then was charged with an own goal on a chaotic sequence three minutes into the second half. Twelve minutes later, a breakdown on the midfield flank liberated Columbus’s Sebastian Miranda, who set up Eddie Gaven for a diving header.

“We work our tails off to get the lead and then we blow it and come out of here with nothing,” said rookie Perry Kitchen, who was part of a makeshift back line necessitated by injuries to three regulars. “It’s hard to swallow. Fortunately we have four games left, but we can’t keep relying on games in hand. We have to take care of business now.”

United might have to win three of its final four to ensure a playoff berth, but given the tangle of teams in MLS’s Eastern Conference and the convoluted wild-card race bridging both divisions, it’s impossible to chart a specific course. D.C. is two points back for a wild-card spot, and has played fewer games than all other challengers.

That said, the club continues to falter when presented with golden opportunities — and the losses seem to be taking a toll on morale. Four days after a 3-2 defeat at Philadelphia, the players filed out of a silent locker room while Coach Ben Olsen conferred with team President Kevin Payne and General Manager Dave Kasper behind the closed door of a side office.

“The guys — most of the guys — put a lot of effort into that game,” Olsen said. “It’s not easy playing a couple days after a big match in Philly. A lot of guys pushed themselves to the limit and I was happy they did. They showed a lot of heart. It’s still disappointing.”

Olsen doesn’t single out players in public, but he was undoubtedly disappointed in Santino Quaranta, who missed a supreme opportunity in the first half and was beaten badly in the build-up to Gaven’s goal.

Woolard’s goal came on a seven-yard volley, set up by Dwayne De Rosario’s free kick. With center backs Brandon McDonald (suspension), Dejan Jakovic (hamstring) and Ethan White (knee) unavailable, Woolard, a left back, joined Kitchen, the usual right back, in the middle. Chris Korb made his first start since June, replacing Kitchen.

Woolard was in the mix on a confusing sequence that led to the equalizer. Columbus played the ball to Andres Mendoza at the top of the box. He turned past two defenders, and as he attempted to shoot, Korb challenged from the side, deflecting the ball toward Woolard. Instinctively, Woolard kicked at it — and sent it past Bill Hamid.

“It happened so fast,” he said. “It was just reaction. It comes off you wrong and is just unlucky.”

In the 60th minute, Columbus went ahead when Miranda burned Quaranta and raced unimpeded down the flank. He targeted the unmarked Gaven, whose contorted header beat Hamid to the top right corner.

The ball was delivered so low, Gaven had the option of using head or foot. He lowered himself so far to make contact, his legs kicked up behind him like a scorpion’s tail.

United’s Andy Najar threatened twice late, but Will Hesmer blocked a distance bid and the teenager’s rasping drive from 14 yards in added time struck the crossbar.

“We’re probably going to sulk a little bit after this one but we’ve got to erase this from our memories,” forward Charlie Davies said. “Now every game is like a must-win.”

United notes: Defender Devon McTavish, who was sidelined for months after suffering a preseason concussion, was included on the gameday roster for the first time this season. . . . United is off until Oct. 12 at Vancouver. De Rosario (Canada) and Hamid (United States) will report for national team duty.