Jordan McRae added 14 points for the Volunteers (21-11), who will play top-ranked Florida in the semifinals on Saturday.
Brenton Williams ended with nine points for the Gamecocks (14-20), who shot just 27.1 percent from the field. Mindaugas Kacinas and Duane Notice each tallied eight points.
Tennessee raced out to a 12-2 lead and never looked back. After South Carolina cut the gap to 18-14, the Volunteers used a 7-0 spurt to build an 11-point margin.
The Volunteers held a 28-18 edge at the break and led by as many as 18 in the second half.