San Jose's playoff chances are rapidly shrinking after it was beaten for the fourth straight game.
The vistors started the scoring early. Eddie Johnson converted a 12-minute penalty to notch his second goal of the year, burying a low spot kick after Brandon Barklage handled the ball in the box.
The Black-and-Red were up 2-0 in the 25th minute. Chris Rolfe's near-post cross from deep was touched to the far post past Jon Busch by Luis Silva.
San Jose pegged one back in the 39th. Chris Wondoloski's rare diastance effort deflected off a United defender and fooled Bill Hamid as it looped into the net.
United goalkeeper Bill Hamid was impressive to preserve the lead as San Jose looked to work its Goonies black magic, coming up with a handful of close reflex saves in the dying minutes.
The loss is the fourth straight for the 4-8-4 'Quakes, but ends a 354-minute scoreless streak. They're now last in the Western Conference and nine points behind the last playoff spot. D.C. is first in the east with a 9-5-4 record.