Sindarius Thornwell scored 13 points, Laimonas Chatkevicius scored 12, and Duane Notice added 11 for the Gamecocks (3-5).
Brad Waldow scored 20 points to lead the Gaels (9-1). Beau Levesque scored 15, Stephen Holt 14 and, James Walker had 13 in the loss.
The Gaels, who trailed by six at halftime, rallied to tie the game three times early in the second half but could not take the lead. The Gamecocks countered every time the Gaels scored and got of help from nearly everyone as nine of 10 players scored in the game.
South Carolina scored six straight to extend its lead to 68-60 with five minutes remaining. The Gaels cut the deficit to 70-68 after Levesque's basket with 2:57 left, but Johnson responded with a 3-pointer for a 73-68 lead with 2:11 left. The Gaels got no closer than four points the rest of the game.
Down 75-71, Walker rushed a 3-point attempt and missed with 28 seconds remaining. After Thornwell hit two free throws, Notice intercepted a pass.
The Gamecocks led by as much as 12 in the first half. The Gaels went on an 8-2 run in the final 1:33 of the first half to close to 33-27 at halftime. It was the first time the Gaels trailed at halftime this season.