The Red Storm (8-1) held the Antelopes to 30.3 percent shooting from the field and forced 21 turnovers that turned into 22 St. John's points.
That defensive intensity buoyed St. John's through some offensive lulls of its own. The Red Storm shot 39.6 percent from the floor and endured scoring droughts of 4:24 in the first half and 2:55 in the second half.
Between its stifling defensive effort and 28 points from sophomore guard Shamorie Ponds, however, St. John's led for all but 3:31 of the game.
The Red Storm lead swelled to as much as 16 points after redshirt sophomore guard Justin Simon laid in two of his 17 points off a Grand Canyon turnover with 6:57 remaining.
The Antelopes (5-2) responded with a late 10-2 run but could not cut the deficit below seven points. They closed the game 1 of 10 from the floor and missed their last six shots from the field.
Senior guard Casey Benson led three Antelopes in double figures with a career-high 18 points. Redshirt senior guard Josh Braun scored 13 points, and freshman forward Roberts Blumbergs added 10 points.
Senior forward Keonta Forward pulled down a game-high 15 rebounds for Grand Canyon but scored no points.
Redshirt junior forward Marvin Clark II joined Ponds and Simon in double figures for St. John's with 10 points before fouling out.
Simon had a double-double with a team-high 11 rebounds. Red Storm senior swingman Bashir Ahmed scored seven points and grabbed 10 rebounds.
St. John's was without redshirt sophomore Marcus LoVett, who was sidelined due to a knee sprain.