Julian Gressel, red-hot Venezuela international Josef Martinez and Jacob Peterson were on target as Atlanta — which became the first expansion side since 2009 to reach the playoffs — extended its unbeaten streak to seven games, a run that has resulted in five clean sheets and 24 goals scored.
More than 43,000 fans packed into the new Mercedes-Benz Stadium, where Gressel opened the scoring with the outside of his boot in the 27th minute.
It's truly a party in the— Atlanta United FC (@ATLUTD) September 28, 2017
Relive the historic night: pic.twitter.com/eykyvYV4EH
Martinez's 18th goal of the season made it 2-0 six minutes later after the Venezuelan forward rifled a powerful low effort across Union goalkeeper Andre Blake and into the net.
After Hector Villalba's second-half goal was ruled out following a video review, Peterson came off the bench to complete the scoring with two minutes remaining.
Atlanta is third in the Eastern Conference as the club prepares to join Supporters' Shield leaders Toronto FC and New York City FC, which edged the Montreal Impact 1-0 on a Jack Harrison strike, in the postseason.
Before we get this second half started enjoy some magic from our . pic.twitter.com/3vzRXVk0Qo— Orlando City SC (@OrlandoCitySC) September 28, 2017
In his first start in four matches, the 2007 Ballon d'Or winner scored twice to remind the world he is not a spent force.
After Xavier Kouassi was sent off in the 11th minute, Orlando took control thanks to 35-year-old captain Kaka, who netted in either half.
The pick of the bunch was his stunning effort from outside of the box two minutes before half-time in Orlando.
The struggling LA Galaxy surrendered 2-0 and 3-1 leads as Alberth Elis scored twice in four minutes to rescue a dramatic 3-3 draw for Houston Dynamo, while the New York Red Bulls and D.C. United also shared the spoils following a 3-3 thriller.