It was the 16th straight victory for Memphis (19-6, 7-3 Conference USA) in the series, as the Tigers weathered a 12-point first-half lead by the Golden Eagles (18-6, 7-4).
Barton had a pair of layups in the final minute and Chris Crawford added a pair of free throws with 5 seconds left to seal the victory.
Southern Miss' Gary Flowers, the conference's leading scorer at 20.2, scored 14 before fouling out with 4:50 left. D.J. Newbill also had 14 points and Maurice Bolden finished with 13 points and eight rebounds.
The Golden Eagles have won a game in the series since 2004, and their last road win over the Tigers was in December, 2000.
They had even more incentive in this one.
Memphis won 76-75 at Southern Miss on Jan. 19, when Charles Carmouche hit a 3-pointer with 1.2 seconds left.
On Saturday, Southern Miss jumped out to a 12-point lead by dominating the boards. The Golden Eagles grabbed a 9-2 rebounding advantage, including six on the offensive glass.
Flowers' bank shot with just less than 10 minutes left in the half helped stake Southern Miss to a 12-point lead.
Memphis responded with 10 unanswered points as the Golden Eagles went more than 4 minutes without scoring. Still, Southern Miss never lost the lead and carried a 37-31 advantage into the locker room.
Newbill had 11 points at that point and Black had 13 to lead the Tigers.
The Golden Eagles rebuilt the lead to double digits early in the second half, and, despite Memphis cutting into it, they didn't relinquish the advantage until just less than 8 minutes left.
Coleman rebounded Crawford's miss to give Memphis a 53-51 lead, the Tigers' first.
From there, the teams remained close, exchanging leads.
Memphis led 63-58 with 57 seconds left when Barton scored on a drive, but Angelo Johnson answered with a 3-pointer for Southern Miss - his only field goal from long range in six attempts -- cutting the lead to 63-61.
Barton added another drive with 20 seconds left to provide enough of a buffer for Memphis' third straight victory.