The No. 1 seeds still have a chance at matching last year's history.
Connecticut, the top seed in the West, and Pittsburgh, No. 1 in the East, both won Thursday night, leaving open the possibility of the four top seeds reaching the Final Four for a second straight year.
When North Carolina, Kansas, Memphis and UCLA all reached the national semifinals last year, it was the first time that ever happened.
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North Carolina, No. 1 in the South Regional this year, plays Gonzaga on Friday, and Louisville, the top seed in the Midwest, faces Arizona.
Connecticut advanced with a 72-60 victory over Purdue, while Pittsburgh moved on with a 60-55 win over Xavier.
The No. 2 seeds had a rough Thursday as Villanova beat second-seeded Duke 77-54 in the East, while third-seeded Missouri beat Memphis 102-91 in the West.
The regional finals are Saturday and Sunday.
STILL BIG EAST
The Big East had a record five schools in the round of 16, and through Thursday's regional semifinal games, it still had five alive.
The three teams that advanced to the regional finals with wins Thursday were Connecticut, which beat Purdue 72-60, Pittsburgh, which beat Xavier 60-55, and Villanova, which beat Duke 77-54.
Louisville and Syracuse were to play their third-round games on Friday night.
The Big East became the first conference to have three No. 1 seeds in one tournament with Connecticut, Pittsburgh and Louisville doing it this year.
It's the only conference ever to get three teams in a Final Four. Villanova, Georgetown and St. John's all advanced to the national semifinals in 1985.
The Big East is guaranteed at least one spot in Detroit next week since Pittsburgh and Villanova will meet in the East Regional final on Saturday night.
''I think everybody in the Big East likes this, us being in the East and having two Big East teams playing,'' Villanova coach Jay Wright said. ''I know the Big East takes a lot of pride in the conference, we all do. You know what, if we're not going to win the final and not go to the Final Four, I'll be glad it's Pitt, but I hope it's us.''
The last time two teams from the same conference met in a regional final was 2002 when Oklahoma beat Missouri 81-75 in all Big 12 matchup.
It will be the fifth NCAA tournament game between Big East teams. In 1985, Georgetown beat St. John's 77-59 in the national semifinals and Villanova pulled off one of college basketball's biggest upsets two days later, beating the Hoyas 66-64.
In 1987, Providence beat Georgetown 88-73 in the regional final and lost 77-63 to Syracuse in the national semifinals.
Missouri's 102-91 victory over Memphis in the regional semifinals ended the nation's longest winning streak at 27 games. It was the Tigers' first setback since Dec. 20, when they lost 72-65 to Syracuse.
The loss also kept Memphis from becoming the seventh school ever to have four or more consecutive regional finals appearances. The last one to do it was Kentucky, which went every year from 1995-1999. The record is UCLA's 10 straight regional finals from 1967-1976.
''Told them after the game that nothing will take away from what they did. We didn't lose for three months,'' Memphis coach John Calipari said. ''And these guys took on every challenge, but we kind of got punched in the mouth right from the beginning of the game.
''I think there is only one other team that has won as many NCAA tournament games as we have in the last four years. And I think that kind of tells you that in the NCAA tournament we're prepared to play, and obviously we didn't play as well as Missouri today.''
Connecticut's Hasheem Thabeet and Pittsburgh's DeJuan Blair were selected the co-players of the year this season in the Big East and their numbers were almost as close as the voting on Thursday.
The 7-foot-3 Thabeet had 15 points, 15 rebounds and four blocks in the Huskies' 72-60 victory over Purdue.
''It was a terrific performance by our kids,'' Connecticut coach Jim Calhoun said. ''I thought a really good performance by Purdue who, quite frankly, ran into one of the best players in America in Hasheem Thabeet. Beyond that, the game might have been different if we had just a, quote, regular center.''
The 6-7 Blair had 10 points, 17 rebounds, two blocks and three steals in the Panthers' 60-55 win over Xavier.
J.T. Tiller almost tripled his average for the season with a career-high 23 points in Missouri's 102-91 victory over Memphis. The 6-foot-3 junior guard, who came in averaging 8 points per game, was 10-for-16 from the field and made one of two 3-point attempts to lead the third-ranked Tigers to their first regional final since 2002.
''What a game to have it, your career high,'' Missouri coach Mike Anderson said. ''His energy was just contagious. I thought he was like a pit bull in a china shop out there. He was going everywhere, just bowling down everybody. He was wherever the ball was.''
Pittsburgh and Xavier entered their game Thursday night as two of the five best rebounding teams in the country and they played to a stalemate off the boards.
Pittsburgh came in with a 10 rebound margin over its opponents, second only to Michigan State's 10.1. The Musketeers were fifth with an 8.4 margin.
The Panthers won the game 60-55, but both teams had 44 rebounds with Pittsburgh getting 18 on the offensive end, one more than Xavier.
It certainly wasn't even at halftime as the Musketeers led 37-29 and were up 23-16 on the boards.
''We knew Xavier was a physical team and obviously they hit us with the first punch, but we came back in the second half and we made some defensive plays,'' said Pittsburgh's DeJuan Blair, who had 13 of his 17 rebounds in the second half. ''Coach kept saying whoever wins the rebounds will win the game.''
Robbie Hummel carried Purdue in the first half against Connecticut, finishing with 15 points as the Boilermakers stayed within five. The second half was much different as the Huskies shut down the 6-foot-8 forward.
Hummel was 6-for-12 from the field in the first half, including 3-of-7 on 3-pointers. In the second half he was 1-for-5 from the field and missed all three of his shots from behind the arc.
The sophomore didn't attempt a free throw in the game and finished with 17 points as the Boilermakers lost 72-60.
''I got some open looks in the first half. I was fortunate to knock them down. The guys were finding me,'' Hummel said. ''I thought I had good looks in the second half, too, I just didn't make them. Stanley Robinson did a good job, I think.''
Connecticut center Hasheem Thabeet credited the whole team.
''He was effective in the first half. And second half we huddled up the whole team and we said we got to find a way to stop him,'' Thabeet said.