What: U.S. Open Cup

Who: D.C. United vs. Union

When: Tuesday at 7 p.m.

Where: PPL Park

Background: This is a round of 16 game. All Major League Soccer teams earned a bye into the fourth round. The Union defeated Rochester, in penalty kicks, 3-1 after the teams played to a scoreless tie on June 16 in their fourth-round game. D.C. United advanced with a 3-1 victory over the host Pittsburgh Riverhounds. Both Rochester and Pittsburgh are in the United Soccer League.

Most recent MLS game: The Union played visiting Montreal to a 2-2 draw on Saturday. D.C. United played host Toronto to a scoreless draw on Saturday.

About D.C. United: With a 10-5-5 record for 35 points, United leads the Eastern Conference. . . . Former Union midfielder Michael Farfan is out for the game with a right hamstring injury. Also out are midfielder Collin Martin (left groin), defender Sean Franklin (left Achilles tendonitis) and forward Chris Pontius (right calf). . .D. C. United has to play Friday at Seattle, so it will be interesting if coach Ben Olsen will rest several regulars. . .Chris Rolfe leads United with six goals.

About the Union: The Union have a 5-10-4 MLS record. . . . Coach Jim Curtin said at his Monday press conference that he plans to play most of his regulars, especially since the team doesn't return to action until June 11 when hosting Portland. . . . With Brian Sylvestre ineligible to play since he competed earlier this season in the Open Cup with the Carolina RailHawks, the Union will go with either John McCarthy or Andrew Blake in goal. In the penalty kick segment against Rochester, McCarthy stopped three penalty kicks. Curtin says he has made his decision, but won't announce it until game time. . . . Curtin said that forward Fernando Aristeguieta (ankle) is not yet ready to play. Injured midfielders Sebastien Le Toux (knee) and Michael Lahoud (hip) and forward Conor Casey (quadriceps) have a chance to get minutes, according to Curtin. Defender Steven Vitoria (hamstring) will likely be available for selection. C.J. Sapong has a team-high six goals for the Union.

- Marc Narducci