Atlanta United coach Gonzalo Pineda knew something had to change.

The team had simply made too many defensive mistakes in a 4-0 loss to New York Red Bulls a week ago,

On Sunday against the Philadelphia Union, Pineda made a change, shifting from a 4-3-3 formation to what was listed as a 5-4-1, but often played as a 5-2-2-1. It worked. Atlanta United won, 2-0, recording its first clean sheet since June 7 against LAFC and first shutout win since May 17 against Colorado.

Offense has not been the problem, as two goals Sunday moved Atlanta United atop the MLS leaderboards for goals scored with 41. But the Five Stripes also lead the league in goals conceded, giving up 35.

Sunday was a different story. Even missing Miles Robinson to the Gold Cup, Atlanta United’s three center backs (Luis Abram, Juan Jose Purata and Ronald Hernandez) and two wingbacks (Caleb Wiley and Brooks Lennon) combined to stymie the Union attack, holding Philadelphia to just one shot on target. Seven Union shots were blocked.

“We’ve been conceding many goals this year,” Pineda said. “And I thought that just having an extra number there without sacrificing the build up and the way we play and play out from the back and all that, (it was what) we can do to be a bit more solid. And I think it worked.”

Playing three center backs helped shut down the Union in the center of the field, while the wingbacks caused Philadelphia problems out wide, both defensively and in attack. Lennon scored the game’s second goal, cementing the victory.

Pineda said postgame that the change was mainly in response to how the Union line up. Philadelphia typically plays with a diamond formation in midfield, utilizing two central midfielders plus both a defensive and an attacking mid, and Pineda wanted three center backs to combat the Union’s formation.

Goalkeeper Brad Guzan was one of the beneficiaries of the formation change. He was happy with how the formation change was executed.

“Based on how Philadelphia played, especially if you watched them coming into this game, the amount of forward players they put against the opposition’s backline, it gave us a little bit of an added security blanket,” Guzan said. “... Having the extra player in the backline allowed for us to be able to deal with the amount of numbers Philadelphia put forward.”

Union manager Jim Curtin actually switched away from the formation, expecting Atlanta United to use its typical formation. He gave credit to Pineda for the tactics, as he was caught by surprise.

“We thought, with their outside backs in (Andrew) Gutman and Lennon, that was their real advantage when they get forward,” Curtin said. “And we put two sixes (defensive midfielders) in there to take care of (Thiago) Almada. … I think both coaches, I think out of respect for each other’s teams maybe changed a little bit.”

Although the five-back formation worked well against Philadelphia, it remains to be seen whether Pineda will continue to use it. His team utilized it with success last year, but it was largely due to an unprecedented wave of injuries. Former manager Tata Martinez also played with five defenders during Atlanta United’s run to the 2018 MLS Cup championship.