ATLANTA — In the two years since its soccer party kicked off for real, Atlanta United has led a dreamlike existence. In a region few predicted would embrace the sport, it has at last produced, in vibrant fashion, the scenes American soccer fans have long envisioned: games being played in a gleaming new home; tens of thousands of fans standing and singing for 90 minutes; and flags and jerseys dotting not only the stands on matchdays, but also the city’s sidewalks, parks and lawns on the ones in between them.

“This thing came out of the earth,” the Atlanta United owner Arthur Blank said, “and is not going back in.”

Squarely established as the league’s standard-bearer in nearly every aspect off the field since it was announced as an expansion team in 2014 and began playing in 2017, Atlanta United has carefully built an infrastructure that it hopes will be able to sustain high standards for years to come.

And on Saturday night, the team capped a brilliant sophomore season with tangible confirmation of its supremacy, beating the Portland Timbers, 2-0, in the M.L.S. Cup final in front of a league-record 73,019 fans at Mercedes-Benz Stadium for Atlanta’s first title.