Atlanta United’s playoff hopes are in trouble.

Facing a must-win match and starting a game for the first time with its two healthy Designated Players, Atlanta United was beaten 2-1 by D.C. United on Saturday at Mercedes-Benz Stadium.

Jon Gallagher scored a tying goal with a diving header in the 89th minute. Brooks Lennon was credited the assist. The goal equalized one scored by Russell Canouse, who got past Miles Robinson at the back post in the 77th minute to head in a cross from former Atlanta United player Julian Gressel.

But D.C. United scored its winner in the second minute of stoppage time on a left-footed hard shot by Gelmin Rivas into the upper left corner.

The loss keeps Atlanta United at 19 points, and it dropped from 11th into 12th in the East behind Inter Miami because it picked up three points with a 2-1 win against Orlando. Miami’s winning goal was scored by former Atlanta United player Leandro Gonzalez Pirez.

“It’s a very frustrating loss,” Atlanta United fullback Brooks Lennon said. “Heartbreaking loss.”

The top 10 teams will advance to the playoffs. Atlanta United has three games remaining and will be favored in only one (against Cincinnati). It will play at Orlando on Wednesday. The team started Saturday one point behind Chicago, four behind ninth-place Montreal, and one point ahead of 12th-place Inter Miami and three ahead of 13th-place Cincinnati. Montreal, Cincinnati and Chicago play later Saturday night.

“We are well aware that it gave our playoff hopes a knock massively,” Atlanta United interim manager Stephen Glass said.

Glass selected probably his most aggressive lineup on offense with Erick Torres at striker, Designated Players Ezequiel Barco and Marcelino Moreno in a midfield that also included Jurgen, Matheus Rossetto and Mo Adams, and a back four of George Bello, Miles Robinson, Fernando Meza and Brooks Lennon, with Brad Guzan in goal.

D.C. United’s lineup included former Five Stripes Gressel and Yamil Asad in its midfield.

Atlanta United couldn’t get much going in the first 10 minutes. Instead, D.C. United showed first with a shot by Erik Sorga from 10 yards. It was saved by Guzan in the 10th minute.

Atlanta United’s first shot on goal didn’t come until the 31st minute was the result of a free kick given 25 yards away. Moreno took the kick, but it was saved. Atlanta United’s previous two shots weren’t anywhere close to being on goal.

Atlanta United’s most exciting chance came in the 45th minute when Moreno slammed a half-volley from 19 yards. Hamid dove to his left to make the save and send the game into halftime scoreless.

The second half started much the same as the first half ended: without much urgency shown by Atlanta United.

Moreno took a shot from 30 yards that was deflected and saved.

Glass made two changes in the 68th minute to try to find a winning goal. Glass brought on Emerson Hyndman for Rossetto and Gallagher for Damm. Glass made another change in the 75th minute by bringing on Adam Jahn for Torres.

But D.C. United scored first on Canouse’s goal. It’s unclear how he got goal-side of Robinson, but it was an easy header.

Atlanta United answered with Gallagher’s diving header. It was a brilliant pass from Lennon, put behind the back line and in front of Hamid. Gallagher’s run was well-timed to the back post.

At that point, Lennon said that every one of Atlanta United’s players were going for the win.

Still maintaining its defensive shape despite trying to find the winning goal, Atlanta United was carved open by three passes and more questionable defending. Lennon was left by himself to try to mark two D.C. United attackers, and neither Robinson nor Meza tracked Rivas’ move back from the goal toward the center of the penalty box. Atlanta United fell to 0-11-2 when conceding the first goal.

“We were all over them,” Lennon said. “And then we conceded one of their fluke counterattacks. Just very disappointing.”

Atlanta United coming games

Wednesday at Orlando (6-2-4), 7:30 p.m., FS1

Nov. 1 vs. Cincinnati (3-6-3), 7 p.m., FSSE

Nov. 8 at Columbus (8-1-3), 3:30 p.m., FSSE

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