North Carolina, the South Region No. 1 seed, used a second-half surge to defeat eighth-seeded Louisiana State 84-70, and West top seed Connecticut shot 58 percent from the floor to crush ninth-seed Texas A&M 92-66.
Ty Lawson, returning from a toe injury, scored 21 second-half points to power North Carolina to victory.
Tar Heels coach Roy Williams was particularly impressed with Lawson. "He showed why he was the Player of the Year in (our) league," he told reporters.
North Carolina will play Gonzaga in the round of 16 on Friday.
Gonzaga, seeded fourth in the South Region, escaped with an 83-81 win over upset-minded Western Kentucky on Saturday.
Connecticut's next opponent will be fifth seed Purdue on Thursday. Purdue advanced by edging Washington 76-74.
Texas A&M coach Mark Turgeon was impressed by UConn's effort and said: "I definitely think they have a chance to be a national champion."
A.J. Price led the Huskies with 27 points.
In other key games on Saturday, Duke, the second seed in the East Regional, defeated Texas 74-69 and Memphis, the No. 2 seed in the West, crushed Maryland 89-70.
