The Union defeated DC United 3-2 at their temporary home, Lincoln Financial Field, and some of the players were taken aback by the reaction of the crowd, including Andrew Jacobson who dived into the crowd after the final whistle.
"I made eye contact with some of the fans and I just went," said the 24-year-old. "I was hoping for an atmosphere like this, and the fans gave us everything."
Defender Danny Califf, who has played in Denmark, said the Union fans had a European aura about the team, praising them for shwing such great support to the brand new club.
"It was European out there," he said. "Really, to a soccer fan, that's what it's all about. If it was like this the first time, I can't wait to see what it will be like from now on.
"If you can't get up to play in front of a crowd like this, you never will; everyone was cheering, out of their seats, waving flags, banners, cheering, booing, it was fantastic."