With the win, the No. 7-seed Spartans (13-3-3) advance to the NCAA Elite Eight where they will play No. 2-seed Indiana on Friday in Bloomington, Ind. Kickoff is 7 p.m.
The winning goal developed off a Connor Corrigan free kick, which John Freitag redirected onto Fiscus' path. The defender managed to get a foot in before Broncos goalkeeper Drew Shepherd could collect the ball.
Fiscus' second-half strike came after MSU's Hunter Barone leveled it in the 43rd minute, redirecting a pass from the left side delivered by younger brother Giuseppe Barone.
"It was an emotional game, and I thought that we had the combination of playing good soccer along with dealing with a competitive, emotional environment," MSU head coach Damon Rensing said. "We've got to be able to play on that edge and still execute and yet we went down a goal, so it certainly didn't look like the day was going our way.
Western's Pepe Martinez opened the scoring in the 25th minute. The Broncos finish 17-4-1.