The single-elimination Open Cup is a true David vs. Goliath format, as if there were a U.S. Baseball Classic and the Clearwater Threshers could beat the Phillies. (Come to think of it, the way the big-league club is going, that's not a farfetched scenario.)
Anyway, the U.S. Open Cup competition has been around since 1914 - slightly longer than the Union, who made their MLS debut in 2010.
The tourney this year began with 64 teams, including all 16 U.S.-based MLS squads.
One of the Goliaths got hammered Tuesday, when the Carolina RailHawks of the second-tier North American Soccer League defeated the defending MLS Cup champion Los Angeles Galaxy, 2-1.
In fact, the lower-tier teams have been prominent throughout. On Tuesday, the Minnesota Stars, also of the NASL, beat Real Salt Lake, 3-1, in Utah, with many of Real's starters playing. On Wednesday, fifth-tier amateurs Cal FC stunned a full-strength Portland Timbers squad, 1-0, also on the road.
MLS teams received byes in the first two rounds. In the 16 third-round games, MLS teams went just 8-8 against the so-called lesser competition.
Think there weren't a few angry comments in MLS meeting rooms over these results?
There is great tradition with the U.S. Open Cup. Some teams look at it as just an exhibition, but the Union apparently see it as much more.
The win over Rochester on Tuesday at PPL Park did a number of things. First, it gave the team a chance to feel what it was like to score more than once. In MLS play, the Union have scored more than one goal just once this year, in a 3-2 loss to the New York Red Bulls.
Second, it diverted attention from the MLS season, in which the Union are 2-7-2 and coming off Saturday's 1-0 loss to a Toronto team that entered the contest 0-9 in league games.
The win over Rochester no doubt provided the Union confidence, and it also gives them something to play for.
And in a strange quirk, the Union advanced to the fourth round, where they face MLS rival D.C. United in Tuesday's 7:30 p.m. game at the Maryland SoccerPlex in Boyds, Md.
When the Union return to MLS play on June 16 at PPL Park, the opponent will be none other than D.C. United.
Two games in two settings, for different purposes involving the same teams.
Don't expect the Union to hold back in the Open Cup game. Last year, D.C. United beat the Union on penalty kicks in the tournament. So the Union look at this game as revenge and as a chance to start a hardware collection.
"I think you always want to win a trophy, and this club doesn't have one yet," Union assistant coach John Hackworth told reporters Tuesday.
Hackworth said the Union were looking for payback. Does this sound like a team that is going to lie down?
"Again, a cup is a cup, and this one is important," Hackworth said. "We just want to play good soccer every game we play."
That's a noble goal, but for now, the Union faithful will take the team's playing good soccer for consecutive games, whether it's in MLS play or not.
Contact Marc Narducci at 856,779-3225, email@example.com or @sjnard on Twitter.