Despite being its first game, its first under a new manager, being a man down, playing with an 18-year-old goalkeeper and playing a tough opponent in an unfamiliar stadium, there was no panic in Atlanta United’s locker room at halftime of Tuesday’s game at Alajuelense.

Midfielder Santiago Sosa and centerback Anton Walkes said the team’s desire to secure a positive result remained strong.

“That filtered down from the coach (Gabriel Heinze),” Walkes said.

The desire received a boost when Ezequiel Barco converted a penalty kick in the 50th minute. That goal proved to be the game-winner and gave Atlanta United a huge advantage going into Tuesday’s second leg at Kennesaw State.

“If we keep things tight at the back and keep them from scoring that’s a job done,” Walkes said.

Atlanta United is unbeaten in home games (at Kennesaw State, Mercedes-Benz Stadium or Orlando) in four previous appearances in the Champions League and has outscored opponents 9-0.

If it can match that history with that determination and things it learned from its first game under Heinze, Atlanta United should advance to face the winner of the series between Philadelphia and Saprissa.

There are many things it can improve, according to the players.

Sosa said he felt comfortable in a position that he is still learning, but needs to work on when he needs to press and when he needs to sit back. He said he also needs to try to be patient with the ball so that he can find the simpler pass and “bring a little security to the team.” Sosa completed 79.4 percent of his passes against Alajuelense, which is a lower percentage than is typical from the position but may have been affected by the fact that Atlanta United was forced to play with just 10 men for the game’s final 47 minutes after goalkeeper Brad Guzan received a red card near the end of the first half.

Sosa was a part of what started as a triangle that included Walkes and centerback Miles Robinson in the center of Atlanta United’s defense. That triangle, as the game grew long, turned into more of a flat line as the team fought off Alajuelense’s attempts to find a equalizer. The hosts took 13 shots in the second half, putting six on goal, and had the ball 64.4 percent of the time.

Sosa said he knows enough English to be able to communicate with the centerbacks about the tactics and movements that Heinze expects. Walkes said more practice will help.

On defense, there were mistakes. Walkes was forced a couple of times to sprint over and cover for fullback George Bello after he either was caught upfield or Alajuelense simply moved the ball too fast for the defense to react. Robinson needed to do the same a few times.

The biggest mistake was the errant pass made by Barco that split Atlanta United’s centerbacks and forced Guzan to come out and try to tackle an Alajuelense player. That play resulted in the red card.

Still, Heinze praised his defense after the game for its fortitude in difficult circumstances.

“There are all these little details we are trying to learn,” Walkes said. “The more we work on it, the better we will be.”