St. John’s took the first step Sunday on what it hopes is a run to the NCAA Tournament, racing out to a big lead and holding off underwhelming DePaul, 72-64, at the Garden. The real challenges loom starting Saturday at Marquette, followed by the Big East tournament. For now, let’s take a look back at St. John’s victory on Sunday, which snapped a two-game losing streak: – Over the last five weeks, Chris Obekpa has impressed with his improved offensive arsenal and his toughness playing on one good ankle. Sunday was more classic Obekpa: shot-blocking and rebounding. He grabbed 11 boards and rejected five shots — two of them at crucial junctures as DePaul was looking to come all the way back from a 20-point deficit. Billy Garrett Jr., DePaul’s impressive freshman, looked as if he was going in for an easy two that would slice the St. John’s lead to one with 3:50 left when Obekpa pinned the the shot on the glass. He later blocked a Brandon Young shot and made him change the trajectory of another shot attempt, leading to a miss. The sophomore big man has become one of the team’s most valuable players, up there with Rysheed Jordan and D’Angelo Harrison, which is stunning considering his slow start and early-season struggles. – D’Angelo Harrison atoned for his clunker against Xavier with one of his finer all-around performances: a 25-point, 10-rebound, three-assist effort. The Storm started slow, but Harrison energized them, scoring 11 of the team’s first 22 points as they quickly snatched a double-digit lead. He was aggressive taking the ball to the basket and confident in his perimeter jump shot — the kind of play St. John’s will need from its leader the rest of the way. – If everything goes right, St. John’s (19-11, 9-8) could finish fourth in the Big East, which would elevate its NCAA Tournament odds. While the Johnnies are currently in sixth, a full game behind Providence and Marquette, those two teams meet on Tuesday, St. John’s faces Marquette on Saturday and Providence visits Creighton next Sunday. St. John’s has split with Providence and beaten Marquette, so another win over the Golden Eagles would give them the tiebreaker.