Jimmy Gavin scored 16 points with five assists and Keon Johnson scored 13. Zach Price added 10 points and the Eagles (14-6, 6-3 Big South) shot 53 percent, including 10 of 25 from long distance, in winning their fifth straight.
Longwood led 19-9 on Kanayo Obi-Rapu's 3-pointer, but Winthrop launched a 24-2 run - in which Gavin hit two 3-pointers - and the Eagles led 48-32 at halftime on 57 percent shooting.
Longwood gained on an 11-2 run to pull within 67-57 with 4:51 left in the second half, but Winthrop blunted the charge and led by 25 with 1:05 to go after Gavin's dunk.
Obi-Rapu scored 20 points and Khris Lane added 15 with 10 rebounds for Longwood (6-15, 2-6), which shot 33 percent.