Vancouver again turned to its younger players and again earned a win. This time it dampened D.C.'s playoff charge.
Camilo Sanvezzo notched 42 seconds into the contest, bringing his season tally up to 12, two behind Dwayne De Rosario, who missed the match after playing in Canada's 0-0 draw with Puerto Rico on Tuesday.
Long Tan became the first Chinese-born player to score in MLS when he headed home an Alain Rochat cross to kick off the second half.
Just before the hour mark, D.C. pulled one back when Brandon McDonaldo got on the end of a Santino Quaranta free kick.
The result leaves D.C. five points behind the final playoff position with three games left. Vancouver, meanwhile, jumped over the New England Revolution to lift off the bottom of the MLS table.