When the season ended suddenly and shockingly, much earlier than Villanova expected, Kris Jenkins bent over in disbelief near mid-court.

There would be no game-winning shot, no confetti-filled celebration, no more games. The defending champions — and No. 1 overall seed — are done.

On Wisconsin.

After two relatively routine days, madness returned to the NCAA Tournament on Saturday as top-seeded Villanova was bounced from the brackets and the East region 65-62 by No. 8 seed Wisconsin, which added another major upset to its resume and stormed into the Sweet 16 for the fourth consecutive year.

Nigel Hayes scored 19 points, dropping a layup in traffic with 11.4 seconds left, and Bronson Koenig shook off foul trouble and added 17 for the tournament-toughened Badgers (27-9), who will play next week at New York’s Madison Square Garden after knocking off a Villanova team that never found its traction in snowy Buffalo.

“Seeds don’t matter,” Wisconsin coach Greg Gard said. “I told these guys I don’t care where we’re seeded. We have to win six games. Let’s start with these two this weekend.”

Mission accomplished.

Check out other big stories from the first weekend of March Madness

1. No. 2 Seed Duke Upset by No. 7 Seed South Carolina

Wisconsin, Florida, Baylor and South Carolina. That’s what is left of your East region.

The No. 7 Gamecocks pulled off a stunner Sunday night, upsetting No. 2 Duke, 88-81, with a dominant second half in front of a friendly crowd in Greenville, S.C.

The Blue Devils had a 30-23 lead at halftime after the Gamecocks missed 20 of their last 22 field goal attempts before the break. But as cold as it was in the first half, South Carolina was just as hot in the second.

Duke trailed by 10 with under four minutes remaining. A 3-pointer by Jayson Tatum narrowed the deficit to seven, but South Carolina continued to deliver on the offensive end, looking quicker, stronger, and hungrier than the Blue Devils, the champions of the A.C.C. tournament.

Duke’s leading scorer, Luke Kennard, was in foul trouble for most of the second half, and Grayson Allen (18 points) struggled with his shot. With Duke’s loss, there is now only team left from the A.C.C.: North Carolina.

Sidarious Thornwell starred again with 22 points, six rebounds, and five assists for South Carolina, which will now head to New York to face No. 3 Baylor.

2. No. 1 Gonzaga Survives Northwestern Upset Bid

Northwestern gave it a good fight — and at least made the final minutes interesting — but ultimately the tournament’s first-round darling was knocked out by No. 1 seed Gonzaga, 79-73.

In the first half, Gonzaga looked well on its way to coasting to a lopsided win. Northwestern’s shooting was putrid and its defense even worse against the top seed in the West region. Perhaps the emotion of winning in its first N.C.A.A. tournament appearance on Thursday had taken a toll on the Wildcats.

But they responded in the second half by cranking up the defensive intensity. After scoring just 12 points in the first 17 minutes, Northwestern actually outscored Gonzaga, 46-31, in the next 18.

3. Xavier Sends No. 3 Florida State Home

The first double-digit seed has made it to the second weekend.

Xavier, a No. 11 seed out of the West, is moving on to the Round of 16 after an eye-opening win over No. 3 Florida State, 91-66.

The game was close for about 10 minutes and then Xavier just took off. A hot-shooting first half (59.3 percent) continued right along in the second. And a collapsing defense forced Florida State to make outside shots, which it did not (4 of 21 from 3-point range). Trevon Bluiett scored 29 points for Xavier, which has now beaten a team from the Big Ten and the A.C.C. to keep on rolling.

4. No. 2 Arizona Too Much for Saint Mary’s

Another upset averted.

Arizona, the No. 2 seed in the West, held off No. 7 Saint Mary’s, 69-60, to move on to face Xavier in the Round of 16.

The Gaels, who led by one at halftime, put forth a tremendous effort, led again by center Jock Landale, who was a force inside (19 points 11 rebounds).

But man, Arizona has a lot of weapons. Rawle Alkins, Kadeem Allen and Allonzo Trier (14 points) were relentless driving to the rim. Then Lauri Markkanen buried a big 3-pointer from the corner and came back and blocked Landale’s hook shot on the other end. The Wildcat shot 59 percent in the second half. That’s hard to overcome.