The hosts head into this one off the back of a first win in four matches last time out, while their visitors set out to avoid a third straight defeat.
Match preview
DC United snapped a run of two losses in a row by claiming a narrow 2-1 triumph over Seattle Sounders in Sunday's meeting between the sides.
Troy Lesesne's men trailed to Leo Chu's early opener but got themselves back on track just past the half-hour mark thanks to Christian Benteke who went on to complete the turnaround in first-half stoppage time.
As a result, The Eagles have moved up to eighth place in the Eastern Conference of the MLS table, just outside the final automatic playoff place only on goal difference.
Coming up next is the challenge of an opposing outfit who are unbeaten in the most recent five editions of this fixture across all competitions.
Having won two of their last three home matches, Sunday's hosts will be keen to pick up another much-needed victory in front of their fans.
Philadelphia Union were beaten for the second consecutive game following a 3-2 defeat against Seattle Sounders at Subaru Park on Wednesday.
Two goals from Raul Ruidiaz either side of Obed Vargas's strike left Jim Curtin's men with a mountain to climb at half time after which Jack McGlynn and Daniel Gazdag grabbed second-half goals to set up a thrilling final half hour.
With 13 points picked up from nine matches this term, Zolos sit seventh in the Eastern conference standings, level on points with this weekend's opponents.
Unbeaten in each of their last four matches on the road, Sunday's visitors have proven themselves to be a tough nut to crack away from home of late.
DC United Major League Soccer form:
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W
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L
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W
Philadelphia Union Major League Soccer form:
W
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D
L
L
Team News
DC United's Conner Antley is still ruled out with a leg injury and the American is joined on the sidelines by compatriot Russell Canouse.
Theodore Ku-DiPietro is also unavailable for the home side due to a hip problem, although the midfielder is closing in on a return to action.
Philadelphia duo Isaiah LeFlore and Nick Pariano continue to nurse respective knee injuries, while Holden Trent continues to battle with a hand problem.
Daniel Gazdag has found the back of the net in four of his last five matches for the away side, making the 28-year-old one to keep an eye on here.
DC United possible starting lineup:
Bono; Herrera, McVey, Bartlett, Dajome; Peltola, Pirani, Klich; Stroud, Benteke, Murrell
Philadelphia Union possible starting lineup:
Blake; Mbaizo, Glesnes, Lowe, Harriel; Martinez, Sullivan, Bueno, Gazdag; Uhre, Baribo
We say: DC United 2-1 Philadelphia Union
There is little separating the teams heading into this one and Sunday's clash could easily head either way. That said, we just about back the home side to emerge victorious in the end.