Goals from Dwayne de Rosario and Nick DeLeon proved the difference.
D.C. United have reached the Open Cup final for the fifth time in their history after a 2-0 win away against Chicago Fire.
Dwayne De Rosario scored a minute before halftime after Sean Johnson mishandled a deflected shot, and Nick DeLeon padded the lead three minutes out of the break to ensure the result.
The victory means D.C. will travel to Rio Tinto Stadium to face Real Salt Lake on Oct. 1 in the championship match.
Chicago had the better of the chances early, and their best of the half came when an Alex header off of a Patrick Nyarko cross was saved by Joe Willis.
But neither team created an abundance of chances before DeLeon’s 44th-minute shot was deflected high into the air, which Johnson misjudged and fumbled before De Rosario placed a shot past defender Austin Berry.
Just two minutes after the halftime whistle, DeLeon collected a cross from James Riley and snuck the ball past Johnson at the near post with a pretty finish.
Conor Doyle almost added to the Fire’s misery in the 60th minute, but Johnson was able to make a save off a breakaway shot from Conor Doyle.
Chicago rallied in the last half-hour, leaving three at the back and bringing on two forwards and almost pulled one back in the 66th minute when Juan Luis Anangonó fired just wide.
Then, in the 78th minute, Berry pounced on a loose ball in the box and tipped it toward the goal, but the ball was cleared by Perry Kitchen as it headed for the lower corner.