Blue's drive along the baseline and layup as time expired broke a 67-67 tie and hoisted the Golden Eagles (23-7, 14-4 Big East) into a conference co-championship with Georgetown.
Blue finished with 16 points and five rebounds while Jamil Wilson added 14 and eight for Marquette, which finished the regular season on a four-game winning streak.
Davante Gardner contributed 10 points and six boards for Marquette.
Phil Greene IV notched a game-high 20 points for the Red Storm (16-14, 8-10). Jakarr Sampson added 17 points and made four steals for St. John's.
Fifth-ranked Georgetown beat Syracuse 61-39 Saturday to clinch a share of the Big East regular-season championship.