Jakob Gollon had 12 points and a season-high 10 rebounds for the Bears (17-9, 10-3), who have won five in a row and seven of their past eight.
Torrey Craig scored 29 points, Ty Greene had 13 and Ricardo Glenn pulled down nine rebounds for the Spartans (13-14, 7-7), whose season-longest losing streak reached four.
The Bears won the rebound battle 36-30 and had 26 points in the paint to the Spartans’ 16. Mercer shot 9 of 18 from beyond the arc to SC Upstate’s 6 of 24.
Mercer led 13-2 on Thomas’ 3-pointer 5:02 into the game and 31-20 at halftime with Thomas hitting a trey with 6 seconds in the period. The Spartans pulled to 67-59 late but never got closer.