Eastern Conference rivals D.C. United and the Philadelphia Union will meet at RFK Stadium on Sunday in a match that has major playoff implications.

For long stretches of the season, D.C. appeared as one of the favorites to win the Eastern Conference, only to fall off the pace and into fifth place 36 points on the season.

United has lost three of its last four league games, most recently falling to Sporting Kansas City, 2-1, at Livestrong Sporting Park.

"I have to search for the reasons why we had an off night, but I didn't like much about the way we played," United head coach Ben Olsen said. "[Sporting was] better than us in every aspect of the game."

The club was missing Dwayne De Rosario through a shoulder injury and the Canadian is listed as doubtful for Sunday's tilt, placing additional pressure on Chris Pontius to produce the goods up front.

D.C. could be buoyed by the acquisition of striker Lionard Pajoy, who joined Olsen's side this week from the Union in exchange for Danny Cruz.

Cruz will be available for selection for Union head coach John Hackworth. The midfielder will be looking to help the club bounce back from back-to-back defeats after it fell to the Chicago Fire, 3-1, at home last weekend.

"This was an extremely disappointing match by the Philadelphia Union," Hackworth said. "It's not the kind of performance that is acceptable to us in any way, shape or form. That said, I think I have to take some responsibility for that result as well. I don't think our team was ready for Chicago in the first half and clearly that was my responsibility."

The three goals conceded in the Chicago defeat were the most in any match since Hackworth took over on an interim basis, matching the most allowed by the club prior to his appointment.

"The concern is that we've given up two restart goals late in the half, and that's man marking," Hackworth said. "Some of it's where you're turning balls over and things like that that's managing the match, but you're going to have those, and for us to be susceptible like that is not good enough."

Philadelphia heads to RFK fighting for its postseason life. The Union sit second from bottom in the East with 23 points from 21 games and need to pick up points in a hurry if they hope to make a second consecutive postseason appearance.