Xavier (16-10, 7-7 Big East) trailed by nine points midway through the second half, but a 12-4 run made it a one-point game with five minutes to play. Trevon Bluiett had a three-point play to keep Xavier close, but Pointer responded with three points on the other end and Rysheed Jordan hit a trey to give St. John's a six-point advantage with one minute remaining.
Pointer, who shot 9 of 10 overall, dunked with 18 seconds left for the final margin.
D'Angelo Harrison finished with 18 points, scoring 13 of those in the first half. The Red Storm (17-8, 6-6) shot 51.8 percent overall and 13 of 16 at the free throw line.