Gaston had 14 points and 11 rebounds for the Spartans (2-1), who led 43-29 at halftime.
The Lancers (0-2) cut the deficit to eight points on three occasions in the second half. After a layup by Michael Kessens made it 69-61, Norfolk State hit 9 of 12 free throws to seal the win, with Rob Johnson hitting 6 of 6.
Zieyik Estime added 12 points, Pendarvis Williams 11 and Malcolm Hawkins 10 for the Spartans, who shot only 30.8 percent (8 of 26) in the second half.
Longwood, which made only 34.4 percent of its field goal attempts in the first half (11 of 32), improved to 47.1 percent (16 of 34) in the second.
Kessens led the Lancers with 17 points, 15 rebounds and four blocked shots.