Since the clock struck midnight a couple weeks ago, marking the start of St. Patrick’s Day — and the moment when Notre Dame outlasted Rutgers in double overtime, sending its coach, Mike Brey, in search of some celebratory Irish whiskey — the madness of the N.C.A.A. tournament has returned this March.

It had been a minute.

The tournament was canceled two years ago at the start of the coronavirus pandemic, and last year it was so muted — sparse crowds, all the games in a single hub stripped of pageantry, players isolated from families, and fears that the N.C.A.A.’s budgetary bell cow might be waylaid by an outbreak.

So when Notre Dame and Rutgers traded haymakers in that play-in game — which may still stand as the tournament’s most captivating theater — it opened the door for more drama. New Mexico State’s Teddy Allen, the walking (and well-traveled) bucket, flummoxing Connecticut. Erratic Memphis throwing a scare into Gonzaga. Iowa State’s Tyrese Hunter, the freshman from Racine who wasn’t recruited by Wisconsin, helping knock out the Badgers in Milwaukee.

And, of course, everyone’s favorite underdog: St. Peter’s.

The 15th-seeded Peacocks from Jersey City, N.J., cut down Kentucky, dispatched Murray State and sent Purdue packing, turning a roster of mustachioed, bushy haired, no- and low-star recruits into something like America’s team. (A small sample, perhaps, but a sports bar in San Francisco filled with U.C.L.A., Duke and North Carolina fans erupted on Friday when Daryl Banks III sank a late jumper to put St. Peter’s ahead for good against Purdue.)

That it all unraveled on Sunday — not far from the Rocky statue at the base of the steps to the Philadelphia Museum of Art — landed like a Will Smith right hand.

All of a sudden, a tournament that was so tumultuous, so capricious, so egalitarian, had ended up with a Final Four that will carry a familiar, blue-blooded streak to New Orleans this weekend: Kansas, Duke, Villanova and North Carolina.

This will be the eighth championship these schools have combined for since 2008, with each of them winning at least one. And in a symmetrical twist, the championship next Monday night will be the 17th awarded to North Carolina, Villanova, Duke or Kansas since the Final Four first came to New Orleans in 1982.

Watching St. Peter’s players — smaller, slower and less skilled — appear so futile against North Carolina served as a reminder that by the end of this three-week basketball fiesta, talent, like North Carolina’s Armando Bacot swooping in for an offensive rebound, almost always wins out.

The last four champions have been No. 1 seeds, as have 11 of the last 15.

The Associated Press Top 25 preseason poll had Kansas ranked third, Villanova fourth, Duke ninth and North Carolina 19th — the Blue Devils ranked so low only because of their youth. The Tar Heels were not rated higher because their coach, Hubert Davis, was new to the profession.

Duke starts five McDonald’s all-Americans and brings in another off the bench. North Carolina is talented enough that Walker Kessler, a third-team all-American at Auburn this season, left Chapel Hill because he could barely get off the bench.

It is little wonder that Duke and North Carolina, a rivalry with such a rich historical vein, is the main event of the national semifinals. The two programs, whose arenas are less than 11 miles apart along Tobacco Road, will be playing for the 257th time, but the first in an N.C.A.A. tournament.

North Carolina already ruined the Cameron Indoor Stadium farewell to Duke Coach Mike Krzyzewski, who is retiring after this season, his 42nd at the school. Now, the Tar Heels can torment the Blue Devils and their coach again, denying him a sixth national championship.

That game, on the final day of the regular season, was a pivotal point for both teams. North Carolina got off the tournament bubble with the victory and has looked almost unbeatable for stretches of the tournament. The Tar Heels blew out Marquette and blitzed Baylor, winning in overtime after surviving what would have been an ignominious collapse. Caleb Love’s scorching second half carried North Carolina past U.C.L.A. And against St. Peters, the Tar Heels dominated.

For Duke, the home defeat was a reckoning. Gradually in this tournament, the Blue Devils have found a mettle they had rarely shown during the regular season, rallying late to beat Michigan State and Texas Tech, and fending off an Arkansas charge.

“No matter what you do as a coach, they have to show that level of character, and in this tournament it’s really lifted them,” Krzyzewski said on Saturday night, adding, “I loved them before, but now I respect them so much.”

No team’s character has been tested like Villanova’s. The Wildcats grinded out four victories with relentless defense, unbreakable poise and just enough shot making — especially when it mattered most. If they win their third title in the last six tournaments, it will be without their most indispensable player — guard Justin Moore, their best defender, a determined rebounder, a vital offensive cog and a team leader who ruptured an Achilles’ tendon in the waning seconds of Saturday’s win over Houston.

Villanova also went through this last season, losing point guard Collin Gillespie to a knee injury late in the season, yet still advanced to the round of 16, where it led the eventual champion, Baylor, midway through the second half before succumbing. Moore’s injury may be a window of opportunity for Bryan Antoine, an oft-injured former McDonald’s all-American who has rarely earned Coach Jay Wright’s trust, playing only 49 minutes over the last two months.

After detailing how essential Moore has been to his team, Wright said in a video call on Monday that he was thankful for a week to prepare for his absence, tactically and emotionally. “You only have to play two games if you’re really fortunate,” he said. “It’s almost like a bowl game in football.”

Kansas, though it was the only No. 1 seed to advance to a regional final, has hardly breezed. It barely survived Creighton — which had lost center Ryan Kalkbrenner to injury in the opening round — and frittered away a 13-point lead to Providence before prevailing, a pair of Big East schools like Villanova. The Jayhawks trailed 11th-seeded Miami by 6 at halftime on Sunday before blitzing the Hurricanes in the second half.

In the coming days, the matchups will be parsed and the story lines exhausted, but there will be no George Mason, Butler, Virginia Commonwealth or Loyola-Chicago this season. Cinderella has once again left before the end of the ball — the surest sign that college basketball is beginning to feel normal.