I'm not quite sure where this ranks in the realm of upsets, but the BBC seems rightly stunned by soccer power Manchester United being beat 4-0 by third-division Milton Keynes Dons in League Cup play. That's a tournament between the clubs of the top three levels of English soccer, it's not as prestigious as the FA Cup which includes all adult soccer clubs and the Premier League title that goes to their major-league regular season champ.
Still, that has echoes of Virginia-Chaminade and Michigan-Appalachian State (who have a rematch Saturday, albeit with Appy State playing I-A ball this time) where college powerhouses were beat by teams well below their station. There aren't any major sports parallels in the US, since major-league teams wouldn't be playing AA-clubs in a tourney; there aren't even any good parallels outside of baseball, since there aren't pro basketball or football leagues two notches below the NBA or NFL.
This is even weirder since the Dons whupped United. One could understand a 2-1 or 1-0 game, but this would be like ASU taking Michigan down 31-3 or a AA team beating the New York Yankees 13-0.
Manchester United has had an off start to its year so far, getting off to a 0-1-1 start in Premier League play, so something might not be right with the club that I liken to a British version of the Yankees in that they spend like drunken sailors (they just set a record for paying for a player's contract today and that's not out of character) and are rarely far from the top of British soccer.