This is the second time in ten days that Seattle has beaten D.C.
“I’m definitely pretty disappointed that they came in to our house and they beat us twice,” United forward Jaime Moreno told The Washington Examiner.
James Riley lobbed the ball just inside the box to Montero, who hooked a shot with his right foot to the top right corner of the goal past Josh Wicks.
United (8-6-12) still leads a seven-team race for four wild-card spots after their first home loss since a 3-0 defeat to Chivas USA on Oct. 4, 2008.
The clubs in contention are separated by only 4 points.
United's next game is Sept. 27 at 3 p.m. against the San Jose Earthquakes.