DALLAS — The smallest player on the court pulled off perhaps the biggest upset in women’s college basketball history.

Morgan William, all 5-5 of her, nailed a pull-up jumper at the overtime buzzer to give Mississippi State an unfathomable 66-64 win over top-ranked Connecticut on Friday night in an NCAA Tournament national semifinal at American Airlines Center.

The guard nicknamed “Itty-Bitty” had a potential winning shot blocked in the final seconds of regulation but came up huge in overtime to send the Bulldogs (34-4) into Sunday’s championship game against South Carolina.

“During the timeout, Coach told me, ‘Mo, you’re going to win the game,’ ” said William (13 points). “Time was just ticking. I knew at the end of regulation I went in for a layup and they blocked it, so they’ll probably think I’m going to do it again. So I got a little space, jumped up and made the shot.

“I was in shock. I’m still in shock.”

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She’s not alone. After all, Connecticut (36-1) entered the night as the most definitive of favorites. The Huskies were riding a record 111-game winning streak, had won the previous four national titles and had crushed Mississippi State by 60 points in the NCAA Tournament a year ago.

This year, though, the Bulldogs took a 29-13 lead and handed Connecticut its first loss since Nov. 17, 2014.

“This is special,” Mississippi State coach Vic Schaefer said in a postgame TV interview. “This was a gutsy, gutsy performance by our entire team. I don’t have to play them [the Huskies] 100 times, I only got to beat them once . . . It was personal, it had to be. You have to question, when you got beat as bad as we did, we questioned ourselves. We’re going to show the world what we’re made of. We wanted to come out today . . . How many people get a chance to play the same team that beat the ever-loving dog out of you, and you get to play them a year later, on a little bigger stage? What a blessing.”

“When you get to this point and lose, it’s the worst feeling imaginable,” UConn coach Geno Auriemma said. “We came up against a much better team tonight.”

After Victoria Vivians hit a long three-pointer at the shot-clock buzzer to put the Bulldogs ahead 60-59, UConn’s Napheesa Collier tied it with a free throw with 27 seconds left in regulation. The Bulldogs had a chance to get the final shot, but Gabby Williams (21 points) slid over to block William’s drive to the hoop, sending the game to OT.

The Bulldogs took a big blow early in the extra period when Vivians (19 points) fouled out. But they went ahead 64-62 when 6-7 center Teaira McCowan hit a layup with 1:12 left.

UConn got a critical break when MSU’s Dominique Dillingham hit Katie Lou Samuelson in the throat with an elbow and was called for a flagrant foul that gave the Huskies two free throws and the ball.

Samuelson (15 points) made both free throws to tie it with 26.6 seconds left, but instead of holding for a final shot to win, guard Saniya Chong went to the basket with 15 seconds on the clock and lost the ball, setting the stage for William.

“There’s a kid trying to win the game,” Auriemma said. “We go over that scenario a thousand times. It’s the easiest thing to do — look at the clock. Saniya just tried to make a great play. God bless her . . . Just impatient a little bit, that’s all.”

Impatience was UConn’s fatal flaw from the beginning, Auriemma said, the result of an immaturity he said he’s seen all season long, but it didn’t bite the Huskies until Friday night. “We’ve kind of lived a charmed life,” he said. “You know how many times this could have happened and didn’t happen? . . . I knew this was coming at some point. I’m just shocked it took this long to get here.”

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The game was an incredible turnabout from last year’s 98-38 UConn rout. “They took us away from the things we like to do and we didn’t have the kind of maturity you need to win at this level at this time of year,” Auriemma said. “We experienced some of the things a bunch of other kids have experienced against us.”