John Simons' jumper put the Chippewas on top 56-54 with 13:53 to play before Seljaas went on his own 11-1 run-three 3s and a jumper-in a little more than two minutes to put the Cougars up 65-57.
Rayshawn Simmons hit a 3 to bring Central Michigan to within 72-67 with seven minutes left, but a Chase Fischer 3 and Kyle Davis' layup made it 77-69 with 6:02 left.
Fischer scored 23 and Davis added 20 for BYU (7-3).
Central Michigan's Josh Kozinski shot exclusively from 3-point range and was 6 for 13 from beyond the arc to lead the Chippewas with 18 points. Simons added 14 points and nine rebounds for Central Michigan (5-5).
The score was tied at 44 at the half.