Trailing 2-0 at halftime, and down to ten men after goalkeeper Bill Hamid was red-carded in the 17th minute, United created very little going forward in the second half, while Houston continued to attack Joe Willis' goal.
The Dynamo finally made it 3-0 in the 62nd minute as Oscar Boniek Garcia headed Andre Hainault's cross back across goal and into the bottom corner of the net.
Referee Jasen Anno provided the final touch in the 88th minute, awarding a penalty after Danny Cruz took out Calen Carr with a sliding tackle in the penalty area. Brian Ching did the honors, chipping the penalty down the middle.
D.C. United travel to Columbus to face the Crew Saturday. Kick-off is at 7:30 p.m.