At the start of another demanding stretch, D.C. United identified an opportunity Sunday in Nashville to collect at least a point and, through lineup rotation, a deepening bench and growing belief in Hernán Losada’s system, position itself for more riches later in the week.

Those grand plans, however, got off to a rough start with a 5-2 defeat to Nashville SC, ending United’s five-game unbeaten streak and bruising a defensive unit that had been very good for months.

An early lead turned into a two-goal deficit, and after Ola Kamara extended his scoring streak, faulty goalkeeping and general weaknesses sent United (8-8-3) to its second defeat in eight matches.

“What would Ted Lasso say?” wing back Julian Gressel said. “We’ve got to be a goldfish at this point, trying to forget this one quickly, move on. We’ve got to have the belief to go to New England and get points” Wednesday against MLS’s best team, then host Atlanta on Saturday.

C.J. Sapong, a Manassas native and former James Madison University star, scored twice in the first half and substitute Alex Muyl, a former Georgetown Hoya, scored twice in the second as Nashville (7-2-10) snapped a three-game winless stretch and improved to 7-0-5 at home.

Before 20,022 at Nissan Stadium, United conceded a season high in goals and for the first time since May 8 allowed more than two.

“We made many individual and collective mistakes,” Losada said. “Many moments we were defending individually, and when you start to step out and to defend on your own and not as a team against a strong opponent, you pay the consequences.”

The defensive letdowns extended to the very back, where Jon Kempin, starting in place of injured Bill Hamid, did not make any consequential saves. Hamid (hamstring) will not return for several weeks, and the third keeper, Chris Seitz, hasn’t played since May 8.

With United trailing 3-2, Kempin was in position to stop Muyl’s low, 12-yard shot in the 80th minute but let it slip by. Later, Muyl converted a penalty kick.

“They ask a lot of questions of us defensively, constantly,” Gressel said of Nashville, which equaled its scoring total of the previous five matches combined. “It was difficult to deal with at times, and there is obviously breakdowns, certain things [when] we weren’t on the same page. Different mistakes happen — today, unfortunately, more than happened in the past.”

United had gone ahead in the third minute on Frédéric Brillant’s first goal since the MLS Is Back Tournament last summer in Orlando. After Joe Willis made a diving save on Kevin Paredes’s bid, Brillant made a near-post run on Gressel’s corner kick and drove in a six-yard header.

Brillant, a center back, was instrumental at the other end four minutes later, making goal-line clearances in rapid succession, first with his head, then with a foot.

Nashville’s pressure paid off in the 14th minute. Randall Leal was afforded time to lift a cross into the heart of the penalty area, where Sapong headed a 10-yard effort off the left hand of a diving Kempin and into the far corner.

Sapong struck again with a 31st-minute header, set up by Hany Mukhtar’s cross from the end line. Neither Brillant nor Tony Alfaro intervened, and Kempin remained rooted to his line, allowing Sapong to power in a six-yard bid for his ninth career goal in 22 appearances against United.

United’s problems deepened six minutes later, when Mukhtar ran at Gressel and ripped an 18-yard shot that took a slight deflection, streaked over Kempin and caromed in off the crossbar.

Four minutes passed before Kamara answered with his 11th of the season, a close-range volley assisted in sensational fashion by Paul Arriola, who launched a high, diagonal ball into the box.

Kamara scored in his sixth consecutive appearance, the longest such stretch by a D.C. player since Luciano Emilio in 2008.

“Before halftime, we get that hope,” Losada said. “We were in the game for a long period.”

Both teams mounted mild threats throughout the second half before Muyl beat Kempin to all but secure three points.

Despite the setback, Losada was able to reintroduce one attacker and introduce another: Midfielder Edison Flores, the club’s highest-paid player, returned from an injury absence of almost three months, and forward Ramón Ábila, acquired on waivers from Minnesota on Wednesday, debuted. Both entered with about 16 minutes left.

The issues, though, were defensive.

“We move on,” Losada said. “No worries. I will learn from this game. The players will learn from this game. We keep moving.”

Notes: With a quick turnaround before facing the Revolution (13-3-4), starting defender Andy Najar was rested. ...

With the team heading directly to Massachusetts, midfielder Russell Canouse, sidelined since July 17 with an ankle injury, was in the travel party so he could continue his rehab and reintegration. He wasn’t in uniform Sunday and seems on track to return to active duty in the next week or two. ...

Aside from Najar and Canouse, rookie defender Jacob Greene and forward Jovanny Bolívar, a Loudoun United call-up, were not in uniform.