Here’s an article from Soccer America’a Web site that breaks down the format.
Eight MLS teams will vie for two Open Cup slots
The four U.S. Open Cup play-in matches for MLS teams have been finalized with the pairing of Real Salt Lake and expansion club Seattle, to be hosted by the Sounders at the Starfire Sports Complex in Tukwila on April 28.
The winner will face the team that emerges from a matchup of Colorado and Los Angeles, which meet April 7. The other play-in bracket pairs San Jose against New York (April 29) and FC Dallas with D.C. United (April 22).
From those separate brackets the two survivors will join the six MLS teams that amassed the most points during the 2008 regular season — Columbus, Chicago, Kansas City, New England, Chivas USA and Houston – in the Open Cup round of 16. The other eight slots will be filled by teams from the USL (First Division, Second Division, Premier Development League) and United States Amateur Soccer Association.
Though it won the crown last year by beating USL-1 club Charleston, 2-1, in the Open Cup final, D.C. United must come through the play-in rounds if it is to defend its title. Charleston had reached the final by eliminating the Sounders (then in the USL) 4-3, on penalty kicks following a 1-1 tie. Seattle also reached the semis in 2007, losing to FC Dallas, as did another USL club, Carolina, a 2-1 loser to eventual Open Cup champion New England.
The winning team receives $100,000 with the runner-up earning $50,000. The non-MLS team that advances furthest in the tournament wins $10,000. The last non-MLS team to win the trophy was Rochester of the A-League, which beat Colorado, 2-0, in 1999.