Mbamalu made 10 of 19 from the field, hitting 5 of 7 from 3-point range as Louisiana-Lafayette (19-10, 10-6 Sun Belt Conference) shot 61.7 percent from the field and 8 of 12 from beyond the arc.
Shawn Long added 20 points and 10 rebounds and J.J. Davenport scored 11 points for the Ragin' Cajuns, who led 52-27 at halftime. Louisiana-Lafayette held a 47-27 advantage in rebounding.
It marks the fourth time this season that the Ragin' Cajuns have scored more than 100 points and the second against a Division I opponent. Louisiana-Lafayette has now won seven of its last eight.
Ken Williams led South Alabama with 24 points and Augustine Rubit added 17, but the Jaguars (9-20, 3-13) shot just 37.9 percent from the field.