The Montenegrin replaced Maicon Santos in the 57th minute. Just seven minutes later, Boskovic stooped down to head a low cross from Lionard Pajoy into the lower right corner of Dan Kennedy's net.
The goal was Boskovic's first for United. It had taken the former Rapid Vienna man 39 MLS regular season games to record his first tally.
The win moved D.C. United level on points with third-place New York Red Bulls in the MLS Eastern Conference standings (New York has scored three more goals than D.C., which is the first tiebreaker in determining the order of the MLS standings). United moved four points clear of fifth-place Houston -- who lost earlier Sunday to Philadelphia -- and five points ahead of sixth-place Columbus. The top five teams in each conference will make the 2012 MLS Cup playoffs.
United travel to the West Coast next weekend to play the Portland Timbers. Kick-off of that game will be Saturday at 10:30 p.m.