The lopsided win helped the Cougars avenge a 70-41 loss at UNLV (19-6, 8-3 Mountain West) earlier in the season and also gave the Cougars a slight cushion at the top of the Mountain West Conference standings.
The win by BYU (20-5, 9-1) pushes its home court winning streak to 44 games.
In the first half, BYU jumped out to an early lead and then used an 11-0 run to take a 26-13 lead with 6:38 remaining in the opening half. Cummard's old-fashioned 3-point play with less than a second remaining in the first half pushed the lead to 39-23 at the break.
Late in the game, BYU used a 12-0 run, including eight straight by Plaisted, to lead by as many as 29.
The Cougars held the Rebels' leading scorer, Wink Adams, to 2-of-14 shooting for nine points, seven below his season average. UNLV shot only 29 percent from the field compared to BYU's 47 percent.
Corey Baily was the only Rebel to score in double figures with 10 points. Troy Cage came off the bench for UNLV to pull down a game-high 12 rebounds.
BYU dominated down low, outscoring the Rebels 42-26 in the paint.
The Marriott Center was packed with 22,580 in attendance.