Where exactly did it all fall apart for the Red Bulls vs. DC?

HARRISON, N.J. – They were plays that will be discussed ad nauseum by New York Red Bulls fans for the rest of the offseason.

Two plays in particular proved critical in New York's elimination after a dramatic 1-0 loss to archrivals D.C. United in the second leg of their Eastern Conference Semifinal series on Thursday night.

The goal by D.C. rookie Nick DeLeon in the 88th minute may have been the difference and the decision to have Roy Miller take a potentially equalizing free kick instead of captain Thierry Henry was a head-scratcher. But it was two plays prior that changed the course of the match: the red card shown to Rafa Márquez and the failed penalty conversion by Kenny Cooper.

WATCH: Cooper's PK saga

Cooper had his converted first penalty kick attempt but referee Mark Geiger ruled that it be retaken due to encroachment by Red Bulls players led by Thierry Henry. Red Bulls manager Hans Backe saw no problem with Cooper retaking the spot kick.

“Kenny is a very confident guy when it’s about penalties,” Backe told reporters after the game. “He was also the guy that got the penalty and he scored on the first one. I think he has no problem with it, he’s a quite cool guy. I think, mentally wise, it’s no problem for him.”

Red Bulls netminder Luis Robles, however, admitted that the goalkeeper may be the one with the upper hand when a PK is retaken and that proved true as D.C. backup Joe Willis saved a low shot to his left after being beaten down the middle on the fist attempt.

“The nice thing from a goalkeeper perspective is now you’re not the only one whose head is going a million miles per hour,” Robles said. “[The kicker is] in a situation where he may have to second guess himself. But regardless, the 'keeper did well.”

WATCH: Márquez sees red

But the turning point in the game was arguably the second yellow card shown to Márquez for a late slide-tackle on D.C.'s Chris Pontius in the 75th minute.

United was down a man after goalkeeper Bill Hamid was sent off six minutes prior on the the occasion of the PK and the Red Bulls were piling on the pressure. But for the second straight year Márquez was once again ejected in the Red Bulls’ final game to make it 10-v-10.

Backe said after the game it was an "unlucky" incident considering the game seemed to be heading to extra time.

“Of course, we lost our advantage,” Robles said. “Rafa was in a tough situation. Really, their own chances today were off fast breaks and they did well. But of course you want to hold on to that advantage and it’s just unfortunate we weren’t able to.”

Franco Panizo covers the New York Red Bulls for MLSsoccer.com. He can be reached at Franco8813@gmail.com.