The trio combined to make 15 of the Warhawks' 22 field goals. Louisiana-Monroe (3-3) shot 50 percent from the field which included 9-of-20 shooting from 3-point range. Jordon Harris missed just one of his five shots and scored 10 points.
Louisiana-Monroe, winners of three of four -- never trailed. The Warhawks led 38-31 at halftime and Sam Alabakis' jumper with 15:24 left extended it to 45-35. Darius Austin made a pair of 3s to reduce the deficit to four but the Tigers couldn't get closer.
Mannion, who recently reclassified and is ESPN's No.11 overall player in the class of 2019, chose Arizona over Marquette.
He'll fit in with Sean Miller's plans for a faster tempo on offense.
The cream of the crop of American high school basketball will congregate in Colorado Springs from Oct. 5-7, as USA Basketball unveils its newly expanded Junior National Team minicamp in collaboration with the NBA, NCAA and NBPA.