Kevin Ferguson added 15 points for the Black Knights (3-0), who have won three games to open a season for the first time since 2001-02. It's also the first time Army has won three straight against Division I teams to begin a season since a Bob Knight-coached team in 1968-69.
Leading by one point with 11:29 left, Army went on a 14-2 run to go ahead 66-53 with 8:10 remaining.
The Terriers (0-2) got to within 72-71 with 1:55 left. Plomb and Wilson each made free throws and St. Francis' Brent Jones missed a 3-pointer as time expired.