Mosley scored 17 points after halftime. He fouled Southern's YonDarius Johnson on a 3-pointer with 3:13 remaining, and Johnson converted the four-point play to pull within 58-53.
But Mosley scored the last six points - a jumper and 4 of 4 free throws - in the final 1:39 as the Golden Lions (9-15, 7-5 Southwest Athletic) held on for the win.
Southern (14-11, 10-2) missed four 3-pointers out of their last six field goal tries and had a four-game win streak end.
Malcolm Miller led the Jaguars with 11 points, Johnson and Trelun Banks added 10 each. Southern was held to 36-percent shooting (18-50) and hit only 6 of 21 3-pointers.
Tevin Hammond added 15 points for the Golden Lions, who shot nearly 48 percent.
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