Number one seeds Memphis Tigers and North Carolina Tar Heels recorded contrasting wins on Sunday to join top-ranked Kansas and UCLA in the Sweet 16 of the NCAA tournament.

While the top-seeded teams in each of the four regions followed the form book, the opening weekend of March Madness concluded with nail-biting finishes and upsets.

The Tar Heels, led by 20 points from Wayne Ellington, completed a weekend stroll through the East Regionals with a 108-77 win over the ninth seed Arkansas Razorbacks.

But in the South Region the Memphis Tigers were forced to fight off a gritty challenge form the eighth seed Mississippi State Bulldogs 77-74.

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Derrick Rose and Chris Douglas-Roberts each contributed 17 points to the Memphis win as the Tigers clawed their way into the last 16 for the third consecutive year.

"You figure, we got them down 13, 14 (points) and they start going away but they (Mississippi) just come right back at us and never stop," Memphis coach John Calipari told reporters. "They just battled us."

Second seeds Texas Longhorns and Tennessee Volunteers also strained their supporters' nerves seats with cliff-hanging wins while the Midwest number two seed Georgetown Hoyas had their championship dreams crushed with a shock 74-70 loss to 10th- seeded Davidson.

Davidson and 12th-seeded Western Kentucky Hilltoppers and Villanova Wildcats provided the surprise story lines of the opening rounds with their unlikely marches into the Sweet 16.

Trailing by 17 points, Davidson rallied behind sophomore Stephen Curry, who scored 25 of his 30 points in the second half to send the Wildcats to Detroit and a meeting with Midwest third seed Wisconsin on Friday.

Tennessee narrowly avoided joining the Hoyas at the exit, battling to a 76-71 overtime win over seventh-seeded Butler in an East Region clash while Texas, led by 26 points from A.J. Abrams, held off the seventh seeded Miami Hurricanes 75-72 in a South regional matchup.

"I've coached a lot of teams and this has been my most resilient team," Tennessee coach Bruce Pearl told reporters. "They do find ways to win and I think it's because this is a close team, there terrific chemistry, we have too many weapons and they count on one another."

In a matchup of Midwest Region giant-killers, Villanova brushed past 13th seeded Siena Saints 84-72 to set up a last-16 showdown with number one Kansas Jayhawks in Detroit.

Scottie Reynolds poured in a game high 25 points and pulled down eight rebounds to help send the Wildcats into the final 16 for the third time in four years.

Courtney Lee dropped in 29 points to pace Western Kentucky to a 72-63 win over the San Diego in the only West Regional matchup on the schedule setting up a meeting with number one seed UCLA next weekend in Phoenix.