Trailing 78-77 with 30 seconds left, Boyd's jumper put the Blackbirds (19-7, 13-1 Northeast Conference) up for good with 18 seconds left. Akeem Johnson then turned the ball over on St. Francis' final possession, and C.J. Garner made two free throws to seal it with 1 second to play.
After beating St. Francis 86-77 on Feb. 8, the Blackbirds won their fifth straight in a game that featured 12 ties and 12 lead changes.
LIU trailed 43-41 at halftime, after getting 13 of Garner's 15 points, and outscored the Terriers 11-2 on fast breaks in the second half.
Jason Brickman added 12 assists for the Blackbirds.
Johnson paced the Terriers (13-12, 10-4) with 23 points.