Ole Miss (22-13) advanced to a quarterfinal game at home Tuesday against the winner of Sunday's game between Georgia Tech and Belmont.
Deandre Burnett, who added 19 points and nine assists, hit the go-ahead 3-pointer with 3:26 left after Andrew White III made a 3 to tie it 74-all.
Burnett was 5 for 9 on 3s, and the Rebels were 15 of 33 from beyond the arc against Syracuse's zone defense.
Cullen Neal had 15 points for the Rebels and Sebastian Saiz had 10 points to go with 12 rebounds for his 22nd double-double of the season.
White and Taurean Thompson led Syracuse (19-15) with 18 points apiece. Tyus Battle added 17 points and Tyler Lydon had 15 points and 14 rebounds.