Notre Dame closed a mostly dominating first half on a 9-0 run to lead St. John's 44-25 at the break.
The Red Storm shot only 37 percent in the opening half as they struggled to find a comfort zone in Purcell Pavilion. St. John's went 3 for 13 from the field in the first nine minutes and finished the first half 10 for 27.
Notre Dame also got off to a slow offensive start, taking a 7-4 lead in the first five minutes.
But Irish guard Ben Hansbrough ignited the offense with three three-pointers during an 11-3 run to give Notre Dame an 18-7 lead with 11:45 to play in the first half.
St. John's started to get a little better on offense from there, but the Red Storm never cut the Irish's lead to below nine in the first half.
Hansbrough went 4 for 6 from the field and 3 for 4 on three-pointers in the first half for 13 points, and Tim Abromaitis scored 10 for the Irish.
St. John's D.J. Kennedy scored six points to lead his team at the break.