Tim Parker (right) celebrates his first-half goal with Kaku. (Eric Hartline-USA TODAY Sports)

CHESTER, Pa. — It’s the MLS Cup Playoffs and you know what that means, Red Bulls fans: More disappointment for a team that has written the manual on postseason failure.

Say this about the Red Bulls, they keep coming up with more ways to exit the playoffs.

On Sunday, they added a new wrinkle: They lost a sizable lead on the road.

After securing an impressive 3-1 halftime lead, the sixth-seeded side allowed it to slip away as the Philadelphia Union recorded one of the great comeback victories in the league’s 24-year playoff history. It also was one of the great collapses in MLS playoff history as well.

Marco Fabian scored from a difficult angle from the left side of the penalty area past goalkeeper Luis Robles in the 105th minute to climax a remarkable two-goal comeback for a 4-3 Philadelphia triumph at Talen Energy Stadium.

Fabrice-Jean Picault sent a right-wing cross toward Fabian on the left side and the Philly player somehow landed a shot into the upper right corner as the Union won its first postseason match in five tries. The team had lost the previous four.

The Red Bulls? They have been eliminated from the playoffs by 10 different teams in the past 10 years.

The Union advanced to the conference final as it will face defending champion Atlanta United at Mercedes-Benz Stadium in Atlanta Thursday night.

No one in his or her right mind could have choreographed what transpired in the match.

The underdog Red Bulls cruised a 3-1 halftime advantage before the Union came roaring back in the second half.

Kaku wound up in the middle of both of the Red Bulls’ first two scores.

The first came in the sixth minute as Josh Sims tallied off passes from Kaku and Marc Rzatkowski.

Kaku found Daniel Royer, who fed center back Tim Parker. Parker connected past goalkeeper Andre Blake in the 24th minute.

Six minutes later, Philly equalized on Alejandro Bedoya’s goal, but forward Tom Barlow restored the Red Bulls’ two-goal margin four minutes into stoppage time.

The Union pressed for most of the second half and its efforts first paid off when Jack Elliott sliced the lead to 3-2 in the 52nd minute.

The hosts weren’t finished as most of the late-match traffic was one way as Picault finished a Sergio Santos right-wing cross from six yards past Robles to complete a stunning comeback to knot the match at 3-3.

Two minutes into stoppage time, Robles produced a reaction save on Picault to keep the game even.