Gleirscher won Austria's first gold medal at the luge in fifty years, while Mazdzer took the silver medal.
No American had medaled in men's singles luge since the event's introduction to the Olympics in 1964, but Mazdzer sat in fourth place after Saturday's two runs at the PyeongChang Games.
The luge event is four runs, and after the first two, Mazdzer was fourth, just 0.001 seconds behind Roman Repilov of Russian Federation.
Mazdzer, a 29-year-old from MA in his third Olympic games, essentially clinched the medal stand yesterday with a terrific third run.
Mazdzer is a three-time Olympian, having finished 13th in both 2010 and 2014.
Mazdzer set a course record in the third run with a time of 47.534 seconds, putting him into second place behind Germany's Felix Loch going into the 4th and final run.
Competing in his third Olympics, Mazdzer, 29, followed up two impressive runs on Saturday with an even better performance on Sunday.
Loch, who also won gold with the German relay team in Sochi, still stands a chance of becoming the first luger to win four Olympic gold medals as a member of the relay team in Pyeongchang.
Erin Hamlin became the first American to medal in women's luge when she took home the bronze at the Sochi Olympics in 2014.
Born in Pittsfield, Mass., Mazdzer grew up in Saranac Lake, N.Y., a 15-minute drive from the U.S. Olympic Training Center in Lake Placid.
And, he made history early Sunday, winning silver in the men's luge.
On the fourth and final run, Loch did what he had never done before in the Olympic Games - he had a disastrous run.