Matthew Moss completed a three-point play with 2:25 left in the extra period to give McNeese a 77-75 lead and Lance Potier, who finished with 12 points and 11 rebounds, made a layup and three free throws to seal the win.
McNeese State held a 39-29 lead at the break, but Nicholls charged back to take its first lead at the 9:38 mark. The Colonels led 70-68 with 28 seconds remaining in regulation and McNeese State's Jamaya Burr made two free throws to force overtime.
Guidry was 6 of 11 from the floor and made 6 of 7 free throws. Burr chipped in 10 for McNeese State (12-15, 6-10 Southland Conference).