Prewitt shot four of seven from the floor with all of his makes from beyond the 3-point line. The Tribe (1-1) made 8 of 21 long-range shots, bolting to a 20-point lead by early in the second half.
Marcus Thornton led William & Mary with 14 points and Prewitt added 12.
Howard (1-2) crept as close as five points, 54-49, on a pair of James Daniel III free throws with 1:12 left. Daniel paced the Bison with 23 points, the only scorer in double figures.
Howard outrebounded William & Mary 35-31 and had nine steals, but shot just 36 percent from the floor on 18-of-50 shooting. The Tribe wasn't much hotter, making 20 of 48 shots for 41.7 percent.