Can you imagine a Seattle Sounders vs. Seattle Sounders U-23 US Open Cup final?

It's not out of the realm of possibility. And it's the only way an MLS club could ever face its U-23 fourth-division affiliate in the US Open Cup.

The Seattle Sounders and Portland Timbers have yet to enter the fray in the 100th edition of the tournament, but their Under-23 PDL teams are sure making headway, advancing to the second round. The Sounders U-23s travel to face the Charlotte Eagles (May 21, 7 pm ET), while the Timbers U-23s will host the Charleston Battery at JELD-WEN Field (May 21, 10:30 pm ET).

Should they advance to the third round, they will face MLS teams, except it won't be their parent club.

READ: MLS teams learn potential third-round USOC opponents

The U.S. Soccer Federation confirmed that tournament rules ensure U-23 teams cannot be pitted against their first-team parent club until the final of the Open Cup. It's one of the reasons why there is a draw conducted for every USOC round with no fixed tournament bracket.

The rationale behind the decision is straightforward: The clubs share the same owner and the competition seeks to avoid the slightest hint of impropriety.

Should the Sounders U-23s advance, they take on the Chicago Fire on May 28 at Toyota Park, while the Timbers U-23s would host the San Jose Earthquakes on the same day.

The Chicago Fire PDL side were the only Under-23 team affiliated with an MLS side to advance to the second round last year. They lost 2-1 to the Dayton Dutch Lions.