The game was tied at 36 at the half.
Rubit also grabbed nine rebounds, and Xavier Roberson made 4 of 7 from beyond the arc and scored 15 points for the Jaguars (2-0), who beat Florida State 76-71 on Friday in Tallahassee.
Daron Bell led the Crusaders (2-1) with 17 points and Douglass Larue scored 10.
The Crusaders shot 53.8 percent (14 for 26) in the first half to stay in the game, but the Jaguars pulled away in the second half with 60 percent (18 for 30) shooting, including 6 for 12 from beyond the arc after going 0 for 6 in the first half. South Alabama also outrebounded William Carey 43 to 30.
Washington State's trio of Josh Hawkinson, Conor Clifford and Ike Iroegbu have withdrawn from the NBA draft and will play their senior season with the Cougars.
Gonzaga center Przemek Karnowski, who missed most of last season with a back injury, says he is returning for another year.
Wisconsin forward Nigel Hayes has withdrawn from the NBA draft and will return to the Badgers for his senior season.