Villanova took the overall top seed on Selection Sunday, with Kansas, North Carolina and Gonzaga joining the defending national champions on the No. 1 line for the NCAA Tournament.

Not many surprises there, though Duke — left at No. 2 despite a four-win-in-four-night performance in the Atlantic Coast Conference tournament — and Syracuse and Illinois State, who got left out altogether, may have been searching for answers.

Northwestern was plenty happy: Though it was no surprise, the Wildcats were jumping up and down, taking selfies and celebrating after being officially invited into March Madness for the first time in the program’s history. The Wildcats were seeded eighth in the West, and will open against Vanderbilt on Thursday.

With the brackets set, the action begins Tuesday and Wednesday with opening-round games that will include matchups between the last at-large teams invited into the draw: No. 11 seeds Providence vs. Southern California and Kansas State vs. Wake Forest.

The Final Four is April 1 and 3 in Phoenix. Villanova, which won the title last year on a buzzer-beating jump shot by Kris Jenkins, will open its quest for back-to-back titles against the winner of an opening-round game between New Orleans and Mount Saint Mary’s.

Some head-scratchers:

—Wichita State, ranked 20th in the nation in the latest Associated Press poll, was given a No. 10 seed.

—Syracuse, a controversial bubble team that made it to the Final Four last year, was left out this time — its 84 ranking in the RPI and lack of solid road wins dooming its hopes.

—North Carolina got top seeding over Duke despite losing two of three to the Blue Devils, including in the ACC Tournament.

—Illinois State of the Missouri Valley Conference was left out, as the selection committee again mainly shunned the little guys, giving all four of the final bubble spots to teams from the six biggest conferences.

Early candidate for toughest region: The South, with North Carolina, Kentucky, UCLA and Butler the top four seeds.