Dallas equalized after a Philadelphia opener, but the Union triumphed in a penalty shootout to advance to the final of the Open Cup.
Union midfielder Amobi Okugo opened the scoring in the 47th minute, but Fabian Castillo leveled for the hosts in the 81st. After a scoreless extra time, the Union triumphed in the penalty shootout. Zac MacMath denied Blas Perez and Victor Ulloa, while all four Union takers - Sheanon Williams, Vincent Nogueira, Cristian Maidana and Maurice Edu - converted.
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Although at fault for Dallas' goal when his mistimed challenge allowed Castillo a clean break on goal, MacMath will likely go down as the hero of the match, making five saves during the game and stopping FCD twice in the crucial shootout.
"It’s awesome," said Okugo after the match. "It’s a feeling that this club has never had before and I know our fans back home are really excited.
"We’re happy to be able to bring it back home."
The final hosting duties were awarded to the winner of this match with a coin flip at last week's Major League Soccer All-Star festivities, and Philadelphia's PPL Park will be the venue for the deciding game. The Union will face off against the winner of Wednesday's Seattle Sounders - Chicago Fire semifinal.
The 2014 Lamar Hunt U.S. Open Cup final will be played on Sept. 16.