Trailing 37-36 with 14:07 left to play, Robert Morris scored 13 unanswered points, capped by McFadden's layup to go ahead 49-37 with 9:04 remaining.
Shane Gibson's layup with 1:27 left cut Robert Morris' lead to three, 62-59, but the Colonials made four free throws in the final minute while the Pioneers converted just one field goal to seal the victory.
Robert Morris shot just 34.6 percent (9 of 26) in the second half but made 18 free throws in the period compared to Sacred Heart's 11.
Gibson led the Pioneers (5-11, 3-2) with 27 points and six rebounds.
Maryland point guard Melo Trimble, considered a lock to leave the program before struggling in the second half last season, has withdrawn from the NBA draft and will return for his junior season.
Louisville's Chinanu Onuaku, who recently underwent a medical procedure to correct a heart rhythm issue detected during the combine, will keep his name in the NBA draft pool.
Andrew White III will return to the Nebraska men's basketball team next season after removing his name from the NBA draft.