The Leathernecks' season wraps up with a 7-9-5 overall record and the team's second consecutive Summit League title.
Western's offense was shut out in the first half, as the Wildcats held an 11-0 advantage in shots in the first period.
Northwestern (12-5-4) scored its lone goal in the 63rd minute, as Henry Herrill found Nick Gendron in front of the net, who put it away inside the right post.
That goal was the only hiccup for sophomore keeper Yves Dietrich, who was phenomenal in goal all game. He saved seven shots, including several that appeared destined to find the back of the net.
Western's offense started getting into rhythm in the second half, as the Leathernecks took seven shots, led by senior Nathan Bruinsma, with two, but the Wildcat defense seemed impenetrable.
Northwestern advances to the Second Round, where it will take on Marquette on Sunday at 4 p.m.