The Supporters' Shield winners grabbed a massive first-leg win in front of 19,525 at RFK Stadium.
The New York Red Bulls defeated D.C. United 1-0 at RFK Stadium on Sunday, taking a big advantage into the second leg of the Eastern Conference semifinal.
Dax McCarty's second-half header was the difference in a tight affair, in which United failed to get a single shot on goal.
New York had the best chance of a cagey first half. Lloyd Sam's cross wasn't dealt with by United, and Bill Hamid rushed out and saved with his face from Mike Grella's close-range chance.