Birnbaum headed home a cross from Rooney on a set piece, following an Orlando City hand ball, to open the scoring in the sixth minute.
Rooney put away a free kick in the 30th to give D.C. United (3-0-1) a 2-0 lead. He drew a foul, conceded by Dom Dwyer, in the left corner a bent a side-netter past goalkeeper Brian Rowe, just inside the far post. The 33-year-old Rooney has four goals (tied for second in MLS) and three assists (tied for first) this season.
Dwyer scored on a header in the 63rd minute for Orlando City (1-2-2). It was the first goal allowed by D.C. United this season and snapped a 435-minute shutout streak in regular season play by goalkeeper Bill Hamid.
Benji Michel, a 21-year-old homegrown player, made his MLS debut for Orlando City.
Source: FOX Sport