JJ O'Brien scored 18 points, Dwayne Polee II added 15 points on five 3-pointers against his former team and
Skylar Spencer added 10 points and seven rebounds for the Aztecs (27-8), who'll face the South's top-seeded
The Aztecs never trailed in the second half and improved to 6-4 in NCAA Tournament play since 2011 under coach Steve Fisher.
Polee, who transferred from St. John's early in his college career, made national headlines when he collapsed on the court during a game against UC Riverside in December because of an irregular heartbeat. He was 5 of 7 on 3-pointers.
Sir'Dominic Pointer had 21 points and 10 rebounds, and D'Angelo Harrison added 18 points for St. John's, which failed in its quest to win its first tournament game since 2000.
St. John's played without center Chris Obekpa, who was suspended on Sunday for a violation of team rules.
The Aztecs stretched an eight-point halftime lead to 14 early in the second half behind Polee's fourth 3-pointer of the game.
St. John's would cut the lead to eight with eight minutes to play before Pointer picked up his fourth foul with eight minutes left. Coach Steve Lavin elected to leave him in the game, but the Red Storm could never mount a serious comeback.
The Aztecs were 14 of 23 from the free throw line in the second half.
O'Brien was 8 of 12 from the field.
Polee came out hot early knocking down three early 3-pointers — including two off the glass — for an early 13-6 lead. San Diego State was 7 of 16 from beyond the arc in the first half.
St. John's didn't have that same success, missing its first seven 3-pointers.
But the Red Storm was able to stay close behind 13 first half points and six rebounds from Pointer, who did most of his damage getting to the hole on the fast break.