Its opponent will be the winner of the Seattle-Chicago semifinal to be played Wednesday at the Starfire Sports Complex in Tukwila, Washington (10:30 p.m. ET, streamed live on ussoccer.com).
MacMath, whose error late in regulation enabled FCD to tie the game, stopped kicks from Blas Perez and Victor Ulloa on their team’s third and fifth attempts, respectively. All four Union players -- Sheanon Williams, Victor Nogueira, Cristian Maidana, and Maurice Edu -- converted their attempts in the tiebreaker.
After a scoreless first half, the visitor broke through shortly after the halftime interval. Amobi Okugo scored in his third straight game in all competitions against FCD to put the Union in front early in the second half.
Waves of FC Dallas pressure led by Fabian Castillo finally paid off with an equalizer in the 81st minute. MacMath had twice raced off his line to stop Castillo -- once with a kicked clearance a yard outside the box, and once with a dive into the attacker’s feet to collect the ball -- but when he mistimed his challenge several yards outside the penalty area, Castillo skipped around him to slot a shot into the empty net.
The Union, which has never played in the Open Cup final, generated the better chances in extra time. An Edu header went straight to FCD keeper Raul Fernandez in the final minutes after Nogueira had hit the post.
Both teams converted their first two penalty kicks. On FCD’s third attempt, a weak effort by Perez was easily turned aside by MacMath diving to his right. Maidana’s shot just inside the post put the Union in front, and after Zach Lloyd and Edu made their kicks, MacMath flew to his left and deflected Ulloa’s shot.
Aug. 12 in Frisco, Texas
FC Dallas 1 Philadelphia 1.
PHL: Amobi Okugo (Sebastian Le Toux, Vincent Nogueira) 47.
FCD: Fabian Castillo (Blas Perez) 81.
(Philadelphia Union wins on penalties, 4-3)