Michigan State (7-1) fell to an unranked nonconference team at home for the first time in more than a decade.
The Tar Heels took control from the start, never trailed and used a 12-1 run to take a 65-52 lead with 6:02 left.
"Michigan State did not want it that much more than we did," Williams said.
Kennedy Meeks scored 15 points for North Carolina and Brice Johnson had 14. Marcus Paige and Nate Britt added 13 apiece.
Gary Harris had 17 points and Keith Appling scored 13, but both Michigan State guards missed 10 of 15 shots. Adreian Payne had 16 points and eight rebounds for the Spartans, whose last loss at home against an unranked nonconference team was Toledo on Dec. 30, 2002.
The Tar Heels beat a No. 1 team for the first time since March 4, 2006, at Duke, and they have a nation-high 13 wins over top-ranked teams. They've won seven straight against the Spartans, including in the 2009 NCAA final.
Tokoto has taken advantage of an expanded role while P.J. Hairston and Leslie McDonald sit out because of NCAA eligibility concerns.
He blocked a shot early in the second half, got to a loose ball and threw it to Appling while the Spartans player was standing out of bounds and made three straight shots later in the half to help the Tar Heels pull away.
• North Carolina 79,No. 1 Michigan State 65
• No. 5 Ohio State 76, Maryland 60
• No. 7 Louisville 90, Missouri-Kansas City 62
• No. 8 Wisconsin 48,Virginia 38
• No. 14 Villanova 77,Penn 54
• No. 25 Dayton 56, Delaware State 46