And I wrote last week when the draw came out that the Union would host Harrisburg in the quarterfinals if both teams won their fourth-round games.
Well, that's exactly what happened. Philadelphia won at D.C. United, 2-1, and the City Islanders upset the New York Red Bulls, 3-1. Both results came in extra time.
So the two teams will meet at PPL Park in the quarterfinals on Tuesday, June 26 at 7:30 p.m.
I asked the U.S. Soccer Federation for a clarification on why Philadelphia and Harrisburg can play each other even though they are affiliated.
The answer is that they technically aren't.
"Philadelphia and Harrisburg are not considered affiliates for the purpose of facing each other in Open Cup competition," a spokesperson for U.S. Soccer told me.
This is because "neither team has an ownership interest in the other - the relationship is one of cross-marketing and other cooperative efforts."
U.S. Soccer acknowledges that the Union and City Islanders "jointly conduct open player tryouts" and play each other in a friendly match each year.
(This season's meeting is scheduled for Tuesday, June 12 at HersheyPark Stadium. I can't help wondering if it might be a good idea to cancel the friendly, since the Open Cup game is two weeks later. I'd like to think it will give the Open Cup game a little more integrity.)
The key thing here is the lack of cross-ownership. I've never been officially told that the Union have an ownership stake in Reading United, but I've asked for clarification.