Florida State’s players were so jubilant they didn’t quite know where to go, so they ran up into the stands to shake hands with whomever they might find. The program had never beaten a No. 1 seed in the N.C.A.A. men’s basketball tournament before.

But Sunday was a feeding frenzy for the underdogs in this epic tournament as five top seeds went down one after the next.

Xavier, in the West region, became the second No. 1 seed to lose before the Round of 16 this year — the first time that’s happened since 2004. The Musketeers joined Virginia, which was the first top seed to ever lose to No. 16 seed, falling to Maryland-Baltimore County on Friday.

That loss seemed to jolt the bracket. But Sunday made a total mess of it.

No. 2 seeds Cincinnati and North Carolina were eliminated, as were Michigan State, the No. 3 in the Midwest Region, and Auburn, the No. 4 in the Midwest.