CLEVELAND (AP) — Willie Cauley-Stein opened his mouth and words came out. He's not sure he believed them, but he said them anyway.

His freshman season at Kentucky ended in a cramped gym far away from the bright lights of the NCAA Tournament. This wasn't what he signed up for, trying to explain how the defending national champions with another roster stuffed with McDonald's All-Americans had somehow lost to Robert Morris — on the road no less — in the NIT.

"I said that day after we lost that I have never won a championship before," Cauley-Stein said. "I've never won anything or any crazy awards and I'm coming back to fulfill that spot in my heart. To fulfill that emptiness."

The thoughtful 7-foot-1 center with the long arms, guard-like quickness and rapidly improving instincts recalls the moment with conviction now. The journey hasn't always been easy, from the perpetual uncertainty of his freshman year to the cusp of history two seasons later as the emotional rock of an unbeaten behemoth.

Kentucky (37-0) can advance to the Final Four on Saturday with a win over third-seeded Notre Dame (32-5) in the Midwest Regional semifinal. The Wildcats are overwhelming favorites to become the first team since Indiana in 1976 to put together a perfect season.

The seeds for the run were sown that ugly night two seasons ago in coach John Calipari's hometown of Moon Township, Pennsylvania, when Kentucky imploded after center Nerlens Noel's left knee smacked into a basketball support against Florida in January.

Calipari doubled down on his recruiting, developing a team so deep the only losses his players have experienced since falling to Connecticut in last year's national title game have come during intrasquad scrimmages. Cauley-Stein is the only regular remaining from the Robert Morris debacle. He pauses when asked if considers himself a survivor.

"I feel like I'm on a mission," he said.

One that has taken longer than expected in the NBA prep school that doubles as Kentucky basketball under Calipari. Unlike many of his teammates, Cauley-Stein arrived in Lexington less a sure thing than a curiosity. He had the raw materials. What he lacked was the confidence required to mold his game into something better than the sum of his considerable parts.

"He didn't know how good he was," said Kentucky assistant coach Kenny Payne. "We saw a bunch of potential. Every year at the end of the year we were like, 'Wow, Willie, you've made a big jump. Now you have to transfer it over to games and have that same jump.'"

Cauley-Stein seemed to put it together as a sophomore, even if that evolution is difficult to quantify with stats. He averaged 6.8 points, 6.1 rebounds and 2.9 blocks. All that momentum came to an abrupt halt when he turned his left ankle in the Sweet 16 against Louisville. He was forced to watch No. 8 seed Kentucky's run to the Final Four from the sideline, drawing attention for vibrant sartorial choices but little else.

Not the glorious exit he planned, serving as the world's tallest cheerleader as Kentucky fell to Connecticut in the title game. He underwent surgery immediately after the season and surprised Calipari by coming back for one more run even though the pipeline was overstocked with hyper-talented big guys to replace him.

"It bothered him to be hurt at that time of the year," Payne said. "Because the first year was up and down and it finished bad and he got a taste of winning last year."

It was merely an appetizer. The Wildcats haven't lost in 355 days. And while freshmen forward Trey Lyles and Karl-Anthony Towns have been as good as advertised, Cauley-Stein has developed into the turbine that propels one of the best defensive teams in college basketball history. His numbers are modest — 9.2 points, 6.5 rebounds and 1.4 blocks — but there is little doubt he is in charge.

"We kind of feed off his energy," Johnson said.

And perhaps that's the most important step in Cauley-Stein's development. He admits he spent two years wondering if he belonged. It took being around "alpha males" like Julius Randle and twins Aaron and Andrew Harrison to play with swagger.

"He's getting it," Payne said. "It just happens in stages. It happens in flows. Hopefully somewhere down the road he gets it totally, he keeps it and he never loses it because that athlete is special."

A notion Cauley-Stein is growing more comfortable with by the day. There are few 7-footers who can lock down point guards and post up centers. He's one of them. Now all those "crazy" things he promised himself on that miserable night at Robert Morris are coming true.

"Two years ago I was just talking and now I'm living it," he said. "It's sensational."