United (10-1-5), which leads the Eastern Conference, has not lost in 10 matches, and increased its point total to 35.
Freddy Adu scored in the 16th minute, and Christian Gomez scored in the 50th minute for United, which has a 15-point edge over the second-place Wizards (6-6-2) and has not lost since May 6 at Colorado.
The Wizards have lost two in a row following a two-game winning streak.
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