Mason made a 3-pointer that gave Niagara a 60-56 lead and sparked a 14-5 run during which Mason hit two more to put the Purple Eagles up 70-61 with 2:59 left.
Niagara went ahead 47-40 with 14:31 left to play, but Marist took its first lead of the second half at 51-50 on Khallid Hart's layup with 9:47 to go.
The teams exchanged the lead three times and tied twice before Marcus Ware's free throw gave Niagara (6-15, 3-7 Metro Atlantic Athletic Conference) the lead for good at 57-56.
Chavaughn Lewis had 25 points to lead Marist (6-13, 3-6) which shot 28 of 52 from the floor and out-rebounded the Eagles 31-27, but couldn't overcome 16 turnovers.
Jaylen Fisher scored 20 points and No. 20 TCU defeated 22nd-ranked Nevada 84-80 on Friday night in the Hall of Fame Basketball Classic, extending its nation's-best winning streak to 15 games.
As an investigation into the eligibility of suspended USC player De'Anthony Melton continues, Trojans head coach Andy Enfield said the sophomore guard "did nothing wrong."
TCU's Alex Robinson throws a one-handed pass to Jaylen Fisher in the corner for the 3-pointer.