Before intermission, Ayo Akinola took advantage of defensive flaws to score twice, and United’s Júnior Moreno was sent off for a second yellow card.

But four minutes after making his D.C. debut, Federico Higuaín scored on a breakaway in the 84th. And in the first minute of stoppage time, captain Steven Birnbaum won a header off Felipe Martins’s free kick, nodding the ball ahead to Frédéric Brillant for a looping, seven-yard header.

United will resume Group C play Friday against the New England Revolution, which won its opener last week. Group play counts toward the regular season, and this result left United with a 1-1-1 record after splitting its first games in February-March.

Since last August, Toronto (1-0-2) is unbeaten in 13 straight regular season matches (5-0-8). This one, though, felt like a loss.

Doubts about this match finally going forward were put to rest when the team buses arrived about 75 minutes before kickoff and both squads began warm-ups. A day earlier, United showed but Toronto did not amid a positive test to a D.C. player and an inconclusive result from an opponent.

Both have since tested negative but were not permitted to join their respective delegations Monday at the venue, pending further testing.

The concern involving these teams followed last week’s withdrawal of FC Dallas and Nashville SC because of several positive tests. In the wake of those cases and the latest episode, MLS officials said the health and safety protocols are working and, barring major issues, the tournament would continue through the Aug. 11 final.

D.C. and Toronto had been scheduled to play last Friday night, but Toronto’s late arrival, due to testing issues, prompted the league to reschedule it to Sunday morning. The match was then moved to Monday at 9 a.m. MLS is playing early in the morning and at night (8 and 10:30 p.m.) to avoid the brutal afternoon weather.

Still, it was increasingly stifling as Monday’s match unfolded.

Toronto set the tone. United was uninspiring.

The lack of pressure on the ball cost United in the 12th minute. Goalkeeper Bill Hamid’s clearance was settled in midfield by Toronto captain Michael Bradley.

A series of passes amid D.C. passivity left Akinola with a pocket of space. His right-footed strike from the top of the penalty area rose and bent away from Hamid before splashing into the left side of the net.

The 20-year-old forward, a former U.S. youth national team player, had scored once in 12 previous league matches.

Toronto continued to menace. United labored to generate the attack. Two water breaks per half, instead of the typical one in oppressive conditions, did not provide any D.C. relief.

The situation worsened for United in the 44th minute. Under pressure from Alejandro Pozuelo deep in D.C.’s end, Brillant relinquished the ball. Pozuelo pounced, then crossed to Akinola for a tap-in.

Before halftime, United stirred, then committed another awful sin.

Toronto’s Quentin Westberg made a breathtaking reflex save on Ola Kamara’s header from point-blank save. Consistent with the proceedings, United also had a handball claim denied by video replay.

With a second left in stoppage time, Moreno inexplicably crashed into the back of a Toronto player near midfield and received a second yellow card. The ejection left United shorthanded and Moreno suspended for Friday’s match.

Olsen made five substitutions in the second half, resting, among others, Kamara, Julian Gressel and Edison Flores. Kevin Paredes, a 17-year-old homegrown midfielder from South Riding, Va., made his MLS debut. He and Chris Odoi-Atsem injected speed and energy.

Martins was fortunate to avoid a red card in the 71st minute.

The second half was a bore until Martins’s through ball liberated Higuain for a breakaway. Cool on the run, the former Columbus Crew star lifted the ball over Westberg for the 56th regular season goal of his MLS career.

United was alive and, under preposterous circumstances, it stole a point in the dying moments.