It was payback, of sorts, for the Cougars, who were thumped 82-68 at the Marriott Center by LMU last year.
Matt Carlino was the unlikely scoring star for BYU, picking up 21 points on 7-for-15 shooting. Tyler Haws added 20 points and Brandon Davies chipped in 12, his movement limited a bit by a sprained ankle.
LMU's Anthony Ireland, the WCC's leading scorer, battled foul trouble in the second half and was held to nine points.
Even BYU football star Bronson Kaufusi scored a basket, after entering the blowout with 1:39 remaining.
Three-point shooting, which hasn't been BYU's friend this season, carried the Cougars to a 35-20 halftime lead.
Carlino scored 12 points in the first half to lead the Cougars, while Ashley Hamilton had 14 for LMU but finished with just 16.
Haws chipped in 10 first-half points for BYU, after scoring 42 his last time out. Hamilton scored LMU's first 11 points, and the Lions jumped to an 11-5 lead before a 10-0 run by the Cougars brought the crowd to its feet.
BYU's flurry of 3-pointers continued after that. The Cougars missed their first five 3-point tries, then made five of seven.
All told, the Cougars were 10 for 23 from 3-point range after going 2 for 25 in last year's surprise loss to LMU.