The Union (10-7-13) jumped from fourth place to second in the Eastern Conference. Philadelphia - 2-0-3 in its past five games - has 43 points, one behind first place Sporting Kansas City.
Le Toux gave the Union a 2-0 lead with goals in the fourth minute and then again in the 15th minute. He leads the Union with 10 goals, including nine goals in the past eight matches.
But D.C. United responded quickly on Dwayne De Rosario's goal in the 22nd minute. De Rosario leads the league with 14 goals and 11 have come since he joined D.C. United.
Andy Najar equalized in the 30th minute before Farfan put the Union on top for good.
D.C. United fell to 9-9-11 and 5-6-4 on the road. It still has more road victories than home wins, the only team in the league to accomplish that feat.
(Copyright 2011 Philadelphia Union. Reprinted by permission)