WASHINGTON — Braylon Mullins retrieved a loose ball near midcourt and suddenly, improbably, UConn had a chance to win.

As the frantic final seconds unfolded, Dan Hurley figured a timeout would do little good.

“It just felt like the window where you’ve just got to let March Madness take over,” Hurley said. “March magic.”

The Huskies have enjoyed plenty of that through the years, and this might have been their most astonishing win yet. Mullins sank a desperation 3-pointer with 0.4 seconds left to give UConn a 73-72 victory over top-seeded Duke on Sunday, earning the Huskies a spot in the Final Four after they rallied from a 19-point first-half deficit.

The Blue Devils (35-3) led by three before UConn’s Silas Demary Jr. made one of two free throws with 10 seconds left. With Duke playing keep-away to prevent the Huskies from fouling, Cayden Boozer’s pass near midcourt was deflected by Demary, and after UConn came up with the ball, Mullins swished a 3 from 35 feet away.

“We were trying to foul the worst free-throw shooter on the floor, and Silas ended up deflecting the pass,” Mullins said. “I knew I had to put one up. Man, I’m just happy that was the one that went down tonight.”

UConn (33-5) went just 5 of 23 from 3-point range. The fifth will be remembered in Connecticut for generations.

It’s the second straight season to end in a huge collapse for Duke, which was the top overall seed in this year’s tournament. The Blue Devils led by six with 1:14 remaining before falling to Houston in last year’s national semifinals.

“I could not be more disappointed and feeling for our guys, at the same time of just trying to process what happened,” Duke coach Jon Scheyer said. “I don’t have the words. I don’t have the words.”

Hurley is trying to coach the Huskies to a national title for the third time in four seasons, a feat that hasn’t been accomplished since UCLA in the 1970s. UConn now faces third-seeded Illinois in Saturday’s semifinal in Indianapolis.

To get there, the Huskies needed one of the biggest comebacks in regional final history. Only Louisville, which came from 20 down to beat West Virginia in 2005, had a bigger one. Duke led 44-25 late in the first half and 44-29 at the break. That’s now the largest halftime lead in tournament history blown by a No. 1 seed.

Cameron Boozer, who had 27 points for the Blue Devils, fought his way to a basket inside with 28.9 seconds to play, and the next UConn possession used precious time before Demary was fouled.

After he made 1 of 2, the inbound came to Cameron Boozer, who passed out of a double team to Dame Sarr, who then found Cameron’s twin brother, Cayden Boozer, in the middle of the court. Instead of waiting to be fouled, Cayden Boozer — who shoots about 81% from the line — tried for one more pass as Mullins and Demary closed in on him.

“I knew we were the back two guys, and we left whoever was behind us,” Mullins said. “We were just trying to make a play.”

There were two Duke players alone deep, but the ball never got there. Demary was able to deflect it, and Mullins picked it up near midcourt. He passed to Alex Karaban, who gave it back to Mullins. The freshman was in rhythm, but about halfway between the 3-point arc and half court.

Nothing but net.

It will go down alongside the great NCAA Tournament game-winning shots, next to Christian Laettner’s for Duke in the 1992 Elite Eight against Kentucky and Kris Jenkins’ to win the national title for Villanova in 2016. Or Laettner’s shot in the 1990 regional final, which turned another Duke-UConn classic from a loss into a win for the Blue Devils.

“Just another chapter in the UConn-Duke NCAA Tournament dramatics,” Hurley said. “Obviously, a really tough way for their season to end. I thought they played great. I thought they punched us in the mouth with incredible force.”

The Blue Devils smothered UConn defensively for must of the game, in part because the Huskies missed 17 of their first 18 attempts from beyond the arc. When told of that stat after the game, Hurley laughed and held his hands over his face.

“What the hell did you just say, 1 for 18?” Hurley said. “I knew it was bad. I kept asking the assistant coaches, and no one would tell me what it was.”

Tarris Reed Jr. led UConn with 26 points, and, for a while, he had little help offensively. The Huskies gradually cut into their deficit in the second half, though, and a 3 by Karaban pulled them within one with under a minute left.

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UConn has now won 18 consecutive games in the Sweet 16 or subsequent rounds. The last loss for the Huskies in those stages of the tournament came against Michigan State in the 2009 Final Four.

For all the success Duke has had through the years, the Blue Devils now have had hearts broken by UConn three straight times in the Big Dance. The Huskies beat one of Duke’s greatest teams in the 1999 title game and rallied late to beat the Blue Devils in the 2004 semifinals.

This one was a gut punch very much on par with those.