The Union delivered one of the all-time wins in team history on Saturday night at Talen Energy Stadium, coming from behind to deck first-place Atlanta United with a 3-1 win that was full of energy and entertainment.

And combined with Orlando City’s loss at the San Jose Earthquakes in the early hours of Sunday morning, the Union became the first team in the Eastern Conference to clinch a playoff berth — and just the second team in all of MLS.

Brenden Aaronson, Kacper Przybylko, and substitute Sergio Santos scored the Union’s goals, all in the second half, after Atlanta’s Josef Martínez put the visitors ahead just before halftime.

Jim Curtin sent his team out to press high defensively even more than usual, with a front four of Brenden Aaronson, Marco Fabián, and Fafa Picault in midfield and Kacper Przybylko up top. The Union conceded 65 percent of the possession in the first half, daring Atlanta try to pass out of the pressure.

Atlanta accepted the challenge, and threatened to score a few times. Yet the Union (15-8-6, 51 points) put the ball in the net first, with Przybylko finishing off a nice give-and-go with Fabián. The goal was taken off the board, however because Fabián was offside — not by much, but by enough that the call was right.

The visitors then got their goal in first half stoppage time. Josef Martínez finished the sequence off, scoring for Atlanta (15-10-3, 48 points) for the 13th consecutive game.

Ilsinho entered in the 58th minute, drawing a big roar from the announced crowd of 18,510 at Talen Energy Stadium. Three minutes later, there was an even bigger roar when Aaronson tied the game. The Medford native was sprung by a great ball from Haris Medunjanin, and while Przybylko was offside, he was judged to be not affecting the play.

Aaronson departed in the 77th, replaced surprisingly by Sergio Santos. It was the Brazilian forward’s first appearance for the Union since July 14, after missing six games with an ankle injury, and it left Andrew Wooten on the bench.

But the move paid off in exceptional fashion. Kai Wagner sprung Santos down the left wing in the 86th minute. Upon reaching the end line, Santos squared a pass back toward Kacper Przybylko, who smashed an unstoppable shot past Brad Guzan to give the Union the lead.

Two minutes later, Santos scored himself, with Przybylko as provider.

Remember all those years of late-game Union collapses? This was the opposite. It came against one of the most talented teams in Major League Soccer history. It was also the Union’s first ever win over Atlanta, after three losses and two ties in the teams’ previous meetings.

Now the Union stand alone in first place again.

“I think we made a pretty big statement about what the Philadelphia Union are all about tonight,” Curtin said. "A lot of people probably did not expect us to get three points. … I think the score was indicative of the performance.”

Perhaps this time, Curtin’s critics might agree.