Last week, Atlanta United lost 3-1 in the first leg of their Concacaf Champions League tie against Herediano in Costa Rica. The defending MLS Cup champions looked unprepared in Frank de Boer’s first game as manager. Defensively, United were suspect at best, and could have conceded on a couple more occasions, while thankfully escaping with an away goal through Julian Gressel’s deflected strike.

Last night in the return leg, Atlanta United trotted out the same formation and made just two personnel changes to the starting lineup. But a couple of tactical tweaks made all the difference in the world, as Atlanta won 4-0 in the game and 5-3 on aggregate, advancing to the quarterfinals against Liga MX side Monterrey. 

The formation looked similar to last week’s, though it more closely resembled a 5-2-2-1 than a 3-4-3. Brek Shea started in place of the injured George Bello, and Darlington Nagbe got the nod as a center midfielder over Jeff Larentowicz. Defensively, the one change that was made was Michael Parkhurst moved to the middle of the three-man backline, after being exposed last week while on the right. Miles Robinson slid out to the flank and performed well again, having been one of the few bright spots in last week’s loss.

#ATLUTD’s Starting XI vs @csherediano1921 pic.twitter.com/4Vj4mgn2QS

— Atlanta United FC (@ATLUTD) February 28, 2019

With the Mercedes-Benz Stadium already occupied, United were forced to play at Fifth Third Bank Stadium in Kennesaw, was only holds 10,000 people, a far cry to the max of 70,000 plus at MBS. But United came out roaring and already had their first goal within 47 seconds.

Josef Martinez, who missed a great chance for a second goal late in the first leg, pounced on a Herediano mistake to give United the lead in the first minute of the game. Atlanta kept the pressure up, as the Costa Ricans were slow to get out of the gate. Atlanta then possessed the ball for a full minute before Ezequiel Barco fed Gressel for the second goal in the ninth minute.

Just like that, Atlanta were going through as the scores stood. Herediano seemed to snap out of their funk after that and played decently over the remaining 35 minutes of the first half. However, unlike the game in Costa Rica, Atlanta were much more organized and seemed to understand what to expect from each other, which limited Herediano’s chances in front of goal.

Shea created a tap-in for Martinez in the second half, and then a cross from Barco was headed in by Leandro Gonzalez Pirez to provide the final scoreline, as Atlanta advanced in their first appearance in the Champions League.

Key moment. Key result.

Another look at tonight's comeback ? pic.twitter.com/ceVcGrluee

— Atlanta United FC (@ATLUTD) March 1, 2019

Pity Martinez didn’t have a standout performance, but he showed several moments of brilliance that indicate what he’s capable of. The former River Plate man likely will need a couple of more games to get his feet under him before he consistently becomes one of the league’s best players week in and week out.

Barco, much maligned in his debut season, was everywhere for Atlanta on Thursday night, picking up two assists. Herediano isn’t on the same level as most MLS clubs, but if Barco can perform as he did on Thursday, he will show why he cost Atlanta $15 million in last year’s transfer. And Shea, while still having his limitations, had a better game than Bello in the first leg. The MLS veteran got up and down the left-hand flank constantly, aiding the attack on a much more consistent basis over 90 minutes.

All that said, the team that D.C. United face on Sunday might not look remotely close to the side that played on Thursday. With the win, Atlanta will now play Monterrey in the quarterfinals of the competition. The first leg of that series takes place this upcoming Wednesday, with the Five Stripes traveling to Mexico. On short rest, with another important game on the other side, Atlanta might send out a weakened team on Sunday.

It’s difficult to predict what the lineup might be, though. There are no data points for how de Boer will approach this game, but it seems likely that Atlanta will put more emphasis on the Champions League than the first of 34 league games this season. An entire new starting 11 might not be the answer, but four to six different players from the opening whistle might not be out of the question. Of course, that means that Hector Villalba could start against D.C., a player who has plenty of attacking prowess but who has been relegated to the bench so far this year for Atlanta.