Philadelphia’s Freddy Adu, right, shown in action May 26 against FC Toronto, returns to Montgomery County to face D.C. United in the U.S. Open Cup. (Abelimages/GETTY IMAGES)
D.C. United vs. Philadelphia Union

What: U.S. Open Cup, round of 16.

Where: Maryland SoccerPlex, Boyds.

When: 7:30 p.m.

Tickets: $15 in advance, $20 at gate (cash only).

At stake: With a victory, United would play the New York Red Bulls or third-division Harrisburg City Islanders in a June 26 quarterfinal at RFK Stadium.

Outlook: Falling during a lull in the MLS regular season schedule, this match allows both clubs to field starting lineups stronger than typically featured at this early juncture of the 98-year-old tournament. Nonetheless, United is missing MF-F Dwayne De Rosario and D Dejan Jakovic, who are with Canada’s national team for two World Cup qualifiers. International duty will also impact the Union: Gabriel Gomez, a Panamanian midfielder who leads the team with four goals, and D Porfirio Lopez (Costa Rica) are away.

In the third round last week, United won at third-division Richmond, 2-1, in extra time, while Philadelphia defeated third-tier Rochester, 3-0. Union MF-F Freddy Adu, who scored twice in that match, is facing not only his former club (2004-06) but returning to Montgomery County, his home for much of his childhood. Adu celebrated his 23rd birthday Saturday.

Philadelphia and D.C. met in last year’s Open Cup qualifying stage at SoccerPlex, with United winning on penalty kicks after a 2-2 draw. United (8-4-3) is first in MLS’s Eastern Conference and has won five of its past six matches in all competitions. Prior to defeating Rochester, the Union (2-7-2) became the first team to lose a regular season match to Toronto FC this season. It has scored just eight goals in 11 league games.

United GK Joe Willis started against Richmond, but with a long gap between regular season matches, Coach Ben Olsen might turn back to top-choice keeper Bill Hamid in order to keep him sharp. Last year, Hamid made a critical save in the shootout against the Union.

— Steven Goff