Dykstra came up big against D.C. midfielder Santino Quaranta, who collected a loose ball in the middle of the area and launched what appeared to be a winner, but Dykstra was able to deflect the ball away.
Dykstra also teamed with center back Wilman Conde to stop a sure goal by striker Danny Allsopp in the 78th minute for Chicago (8-12-9).
The contest marked the last home game for Fire forward Brian McBride, who is retiring this season after a career as one of the greatest strikers in MLS. McBride had several opportunities to score in his home swan song but couldn't connect.
Troy Perkins made a draw-saving stop for United (6-19-4) in the 89th minute on a 12-yard shot by substitute forward Calen Carr.
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