Justin Satchell's jumper made it 72-67 for the Purple Eagles (3-5) with 31 seconds to play. The teams traded free throws, and Quinnipiac's Giovanni McLean made a 3-pointer with eight seconds left to cut it to 74-72. Blackman made a pair of free throws at the other end to seal the victory.
Satchell added 11 points for Niagara.
Quinnipiac's third-leading scorer, Chase Daniels, left the game early in the first half with an apparent leg injury. He had four points in five minutes.