The Irish used a 12-0 run in the first quarter to break a 4-4 tie and cruised the rest of the way.
Lafayette led 23-10 after the first quarter and led 44-22 at halftime.
Xavier Kurth scored 22 of his game-high 24 points in the first half.
The Irish continued their dominance in the second half as they scored the first 13 points of the half as Caleb Bennett scored all 10 of his points in the quarter and they led 68-32 after three.
Billy Cook added 12 for Lafayette, while Richard Bowen led Benton with 13 points.
The Cardinals fall to 0-3 this season.
Other St. Joseph scores from Tuesday night:
Oak Park 56, Central 43
Jefferson 53, Bishop LeBlond 51
St. Joseph Christian 59, South Nodaway 53
Bishop LeBlond 57, Jefferson 41