Some upsets aren’t as big as the seed lines suggest; some are bigger. Two years ago, the No. 2-seeded Duke Blue Devils were upset by No. 15 Lehigh in the first round of the NCAA tournament. But Duke was the weakest No. 2 seed in 2012, according to the FiveThirtyEight projections that year, whereas Lehigh was unusually strong for a No. 15. Our model had given Lehigh a 10 percent chance of winning.

Something of the same pattern held last season when No. 2 Georgetown lost to No. 15 Florida Gulf Coast in the first round. Georgetown was just the 15th-best team in the country, according to our ratings, and was badly overseeded as a No. 2. Our model gave that upset a 10 percent chance of occurring as well.

This afternoon, as a No. 3 seed, Duke lost to 14th-seeded Mercer — but the Blue Devils (and the FiveThirtyEight model) have fewer excuses. In fact, Duke was the strongest No. 3 by some margin this year, according to our ratings and other indices like Ken Pomeroy’s power ratings. Our projections had Mercer with just a 7 percent chance of winning before the game began.