I really don’t see how ND-SEN 2012 qualifies as an "upset" or a result "no one saw coming." Literally every pre-election poll except one showed an extremely close race (with both candidates trading leads and polling close to 50%), and all the major prognosticators had the race listed as a Tossup (Sabato moved it to Lean R only when they had to pick a winner in each race, Rothenberg only moved it Tossup/Tilt R).
https://en.wikipedia.org/wiki/2012_United_States_Senate_election_in_North_Dakota#Polling_2