O'Quinn broke a 61-61 tie, the 12th of the game, on a jumper with 3:59 remaining to give the Spartans the lead for good. Norfolk State made 10 of 12 free throw attempts the rest of the way. O'Quinn was 7 of 8 from the free-throw line and Williams made all six of his attempts for the game.
Neither team led by more than seven points and there were 18 lead changes.
Marcos Tamares added 16 points for the Spartans (19-8, 10-3 Mid-Eastern Athletic Conference), who have won three of their past four.
Kevin Dukes scored 16 points, Anthony Breeze added 12 Javoris Bryant 11, and Garrius Holloman had 10 points and 12 rebounds for the Wildcats (13-15, 9-4), who had a three-game regular-season winning streak against the Spartans snapped.