De Rosario scored in the 68th minute to pass the milestone and put United ahead 2-1. Nick DeLeon also scored for D.C. (12-9-5), which tied a club record set in 2007 by extending its home unbeaten streak to 13.
New York stretched its unbeaten streak to four matches as it closed to within a point of first-place Sporting Kansas City. The Red Bulls drew 1-1 at Sporting on Sunday.
With time running out and New York pressing for the tying score, a half-clearance trickled outside the 18-yard-box and into the Conde's path. The defender struck a knuckling blast with his first touch into the top right corner and beyond Bill Hamid's dive for his first goal of the season.
De Rosario had put D.C. ahead 20 mijnutes earlier on a header of DeLeon's cross from the right made easier by a poorly timed run by goalkeeper Bill Gaudette. Instead of remaining in his goal, Gaudette came to try and punch away the cross, but was beaten by De Rosario, who had an empty net to aim at.
With the goal, De Rosario became the seventh player, and second active one, to pass the 100-goal plateau in the league's 17-year history.
Lindpere scored in the 19th minute on a drive from the left side that appeared to deflect off Bill Hamid's side and into the right post.
Two minutes later, DeLeon struck back on a somewhat softly struck side-footed volley of De Rosario's cross that somehow squeezed beneath Gaudettes dive to the left.