It was a stunner that busted a ton of brackets.

Villanova, the defending national champion and the top overall seed, was upended by eighth-seeded Wisconsin 65-62.

Fellow No. 1 seed Gonzaga, helped by a blown call that the NCAA acknowledged was wrong but led to a technical foul on a furious Chris Collins of Northwestern, barely survived a charge from the underdog Wildcats.

Eleventh-seeded Xavier routed Florida State 91-66, and Florida did the same in dispatching of Virginia 65-39. Second-seeded Arizona and fourth-seeded Butler each won by nine, and West Virginia opened the day with a 12-point win over Notre Dame.

Purdue and Iowa State capped the day's action with a thriller. The Boilermakers nearly blew a 19-point lead, but held on for an 80-76 victory.

No. 1 seeds North Carolina and Kansas look for Sweet Sixteen bids on Sunday, as will Duke, Louisville, Kentucky and UCLA.