Jalen West and Marvin Frazier scored 18 points apiece for the Demons (17-13), who will play Stephen F. Austin in the semifinals on Friday. Zikiteran Woodley added 11 points and Brison White had 10 points. Frazier, Woodley and White all finished with seven rebounds each.
Jeremy Smith tallied 24 points and eight rebounds for Nicholls (14-15), while Dantrell Thomas scored 12 points. T.J. Carpenter finished 4-of-19 from the floor for 11 points, which he accompanied with eight boards.
Northwestern State connected on 51.4 percent of its field goal attempts, including a 5-of-12 clip from behind the 3-point line in the first half. The Colonels went into the intermission trailing, 43-28, after it was limited to 36.5 percent efficiency from the floor in the opening stanza.
Although the Demons cooled off to shoot just 37.5 percent from the field after the break, they managed to protect their lead by sinking 20-of-28 attempts at the charity stripe. The Colonels hit on only 6-of-22 tries from beyond the arc over the final 20 minutes of the contest.
Northwestern State's reserves outscored the Colonels' bench, 31-11.