Iona hit 54 percent from the floor, including 13 of 27 from beyond the arc. Leading scorer Sean Armand was held to just 11 points.
Siena (7-12, 3-5 Metro Atlantic) trailed by six points midway through the second half when A.J. English's layup kicked-off an 11-2 Iona run capped by a Williams layup giving the Gaels a 70-57 lead with seven minutes to play.
Tavon Sledge's basket inside the paint extended Iona's lead to 17 with 4:40 left, marking the largest lead of the game. The Gaels coasted to the buzzer, winning by 14 points.
Iona (9-8, 6-2) also beat Siena last Sunday 87-78, and has won seven of its past eight meetings.
The Big East has joined the ACC, Atlantic 10 and Colonial Athletic Association in forming a men's basketball officiating alliance.
Nebraska guard Andrew White, who averaged 16.6 points and 5.9 rebounds per game last season, will transfer from the program and is eligible immediately. What else is on Dickie V's mind this week?
The Cavaliers bring in a top-10 class of four incoming freshmen, so the Class of 2017 will be a small one. Coach Tony Bennett is aiming high.