Last night's US Open Cup win qualified D.C. United for the tournament's fifth round, and today's draw has sent them back to the Keystone State to take on the Philadelphia Union. The match will take place on June 30th at 7:30pm in the Union's home stadium, PPL Park. To get to this stage, Philadelphia won a penalty kick tiebreaker after a 0-0 draw with the USL's Rochester Rhinos on Tuesday night.
There have been some changes to how the tournament draw is conducted this year. The final 16 teams left in the tournament were drawn into geographic groups, with United and the Union in the East region with the New York Red Bulls and the NASL's New York Cosmos. The fifth round winners will face the other remaining team in their region, so a United victory will see them play either the Red Bulls or the Cosmos. Hosting rights for that quarterfinal match were already drawn, with the United-Union winner on the road no matter who wins between NYRB and the Cosmos.
Should United win twice and get to the semifinal round, they would hold the option of hosting the match (meaning that DC would have to opt out of hosting to end up traveling again). The host of the final has not been determined yet, and will be determined sometime in the days before the semifinal matches are played.
For the full list of pairings, check out US Soccer's article (which contains video of the draw as well).