The Rams (3-9), who trailed 57-28 at halftime two days ago in an 88-73 loss to Connecticut, were sharp early this time, shooting 69 percent (20 of 29) in the first half.
Gaston scored 20 points as Fordham took a 47-31 halftime lead. The senior forward now has 1,514 points, ninth on the school's career list.
The Saints (2-10), in their first game since Dec. 9, rallied to shoot 60 percent (15 of 25) in the second half. They got within 63-62 with 10:04 left after consecutive 3-pointers by Rob Poole and Rakeem Brookins, but three straight Fordham baskets made it 69-62.
Poole had 21 points, Brookins 18 and O.D. Anosike 16 for Siena.
Bryan Smith added 15 points for Fordham.
Kapita was the top-rated recruit from West Virginia in the class of 2015 and recently played at DME Academy in Florida.
With the Suns drafting Tyler Ulis, they now have five guards on their roster who attended Kentucky.
NBA fans will be looking forward to their newest players making plays like this next season.