Even if Atlanta United hasn’t lost to Miami 3-2 on a goal in injury time, manager Gerardo Martino wasn’t sure the result was going to be different had the game gone to extra time.

He said his team was making too many mistakes, some a result of inexperience, some a result of fatigue and some the result of the quality of Miami.

“With a team like this, you can’t make errors like that,” Martino said. “We made errors but also Miami isn’t a bad team. We paid the price.”

The worst mistake came when Harrison Heath, a seldom-used player inserted into the game just a few minutes earlier, lost the ball, which went to Miami’s Vincenzo Rennella. He sent a pass into space behind Atlanta United’s fullbacks, where Kwadwo Poku, formerly of the Silverbacks and NYCFC, ran onto it and mishit a shot past Alec Kann and into the goal. Kann came out to close down the angle, but Poku took the shot from far enough away that it couldn’t be stopped.

The loss knocks Atlanta United out of the Open Cup.

While Atlanta United now won’t have a chance to win its first trophy, it will have a chance to concentrate on strengthening its spot in the Eastern Conference playoff race. The team is in the sixth and final spot as it begins the second half of the schedule on Saturday at Columbus.

Atlanta United’s goals were scored by 18-year-old Brandon Vazquez and 23-year-old Julian Gressel, with 17-year-old Andrew Carleton making his first start and 18-year-old Lagos Kunga making his debut.

It was going to be a tough game. Miami FC is loaded with players who have MLS experience, including Poku. The team fielded most of the lineup that has helped it run away from the other teams in the NASL Spring race. Miami FC has 30 points, seven more than second-place San Francisco, through 13 games. It was unbeaten in its previous 13 with a plus-18 goal differential.

Plus, it had already knocked off one MLS team, Orlando City, 3-1, in the tournament and this time was playing at home at Riccardo Silva Stadium, where it had lost just once this season.

Martino went with a lineup featuring a balance of experienced and inexperienced. But it didn’t include a lot of goals, just six this season among the 11 starters. He was slightly handcuffed by the Open Cup restrictions of only being able to use five international players. That, combined with some players needing rest, resulted in the Wednesday’s 18.

Among those in the 11 was Carleton. The team’s first Homegrown Player made his first start of the season. The 17-year-old, a native of Powder Springs, had previously played a few minutes at the end of the 4-1 win over Houston.

Here are five observations about the game.

The first goal. Atlanta United took a 1-0 lead in the 35th minute on a header by Vazquez off a pass from Kevin Kratz. It came on a free kick and was the team's first set-piece goal this season. It was Vazquez's third goal in all competitions. Vazquez said he was able to get in front of his marker for the goal.

“In the last month he’s grown tremendously as a player,” Martino said. “In previous games in MLS he’s done very well. We are very happy with him.

The second and third goals. Miami needed two minutes to tie the game. Chris McCann gave away the ball with a bad pass. Poku picked it up and passed it to Stefano Pinho, who only had Kann to beat.

Miami took a 2-1 lead in the 52nd minute on a header by Rhett Bernstein off a free that was result of a Carlos Carmona two-footed tackle. The kick was taken by Hunter Freeman. He curled it in from the left, where Bernstein ran onto it and hit a glancing header.

The gamble. Martino gambled by inserting Kunga, signed to a four-day contract earlier in the day. Kunga, an 18-year-old Atlanta native, will sign a Homegrown Player contract in January. It was also announced earlier on Wednesday that he will play for the Charleston Battery the rest of the season. Martino also brought on Mikey Ambrose, taking off Anton Walkes and Mark Bloom, two defenders.

The move changed the personnel within Atlanta United’s formation. Julian Gressel dropped back into the midfield with Kratz, and Carmona playing beside Leandro Gonzalez Pirez on the back line. Kunga, Vazquez and Carleton floated around as forwards.

The gamble on youth worked when Carleton was tripped by Poku in the penalty box in the 74th minute, resulting in a penalty kick. Gressel drilled the shot to tie the game at 2. It was Gressel's fourth goal in all competitions.

Carleton said he was mostly happy with how he played, but could have been sharper in a lot of areas and wishes he had taken on more defenders. He said the one time he did resulted in the penalty.

Martino said he was very happy with how Carleton and Kunga played. They flew from the Academy playoffs on Sunday to join the team.

Kunga said he wasn’t sure he was going to play until he heard Martino calling his name.

Poku's revenge. Poku remains a fan favorite from his time with the Georgia Revolution (2011-13) and with the Silverbacks in 2014. He's an aggressive, strong, fast player who the fans loved for his style and the Silverbacks' success while he was there.

“I caused the PK that made the match 2-2, but like what coach (Alessandro Nesta) said when we get opportunities we have to take them,” Poku said. “There were many times when we had great chances but the last pass or finish wasn’t there. We believed in ourselves and played great defense at the end and we knew we were going to get there and get that final goal.”