Mitchell had a layup, converted a 3-point play and added three free throws in the extra period. Delaney made a 3-pointer and five shots from the free-throw line as the Bearkats (18-9, 13-1 Southland Conference) outscored Nicholls 17-7 in overtime.
Marcus Harris' layup for Sam Houston State tied it at 67 with 57 seconds left. Each team then missed a 3-point attempt to force overtime.
Mitchell finished with 19 points, 14 rebounds and four assists. Delaney had 15 points, 11 rebounds and three blocks.
Gavin Peppers had 21 points for the Colonels (11-15, 4-9). Elvis Harvey added 10 points and 10 rebounds. Kevin Johnson had 10 points. Jeremiah Jefferson, the Colonels' leading scorer entering the matchup at 16 points per game, had only six points (2 of 12).
Sam Houston State takes on Houston Baptist at home on Saturday. Nicholls State takes on Central Arkansas at home on Saturday.