United States def. Russia – 1980 Winter Olympics Hockey Semifinals:
There just is no other upset that could be listed number one on this list. This is the upset in sports history.
The Russian team was heavily favored to win the gold heading into the 1980 Winter Olympics from Lake Placid, New York, and for good reason. The Russians won five of the six previous Olympic gold medals in ice hockey. They met up with the much less experienced U.S. team in the semifinals.
What happened there was sports history in the fullest sense. The Americans, facing a 3-2 deficit heading into the final period, put two goals on the board to emerge with the miraculous 4-3 victory. The win became known as the iconic ‘Miracle on Ice’ and will almost certainly be the biggest sports upset of all-time for the rest of time.