Desmond Ringer added 16 points for the Bears (16-6, 6-3 Southern), who improved to 10-0 at home before 4,032 fans, the second largest crowd in Hawkins Arena history.
Kayel Locke had 20 points for the Spartans (8-14, 4-5) and Francis Alonso added 14. UNCG made 12 of 29 from 3-point range and 9 of 22 inside the arc.
Stephon Jelks hit a 3-pointer with three seconds left to give Mercer a 35-31 lead at the half. Locke and Marvin Smith opened the second half with 3s for UNCG but the Bears got baskets from Ethan Stair, Lewis and Jelks to open a 52-43 lead with 11:51 remaining. Back-to-back 3s from Cory Kilby and Lewis pushed the lead to 61-48 with 8:55 to play.
Mercer shot 50 percent, including 10 of 22 on 3-pointers.