Nothing done earlier this season by a makeshift St. John’s team that practically was assembled overnight by Chris Mullin and his coaching staff could have prepared anyone for what the Red Storm accomplished yesterday at Madison Square Garden. A crowd of 13,473 that was swelled by Syracuse fans came expecting to see an Orange blowout but got something completely different.

It all came together for the Red Storm, which scored a stunning 84-72 upset of Syracuse that will go down as the first signature win of the Mullin era.

St. John’s dissected the Orange’s famed 2-3 zone, shooting 49.2 percent overall and an even 50.0 percent from three-point range, making 12 of 24.

Syracuse coach Jim Boeheim wasn’t on the sideline to witness it because he is serving an NCAA suspension, but assistant Mike Hopkins came away impressed by St. John’s. “Their staff has done a heck of a job,” Hopkins said. “All those guys got better. They really executed against our zone.”

Just four days earlier, the Red Storm (7-3) was lucky to pull out a 48-44 home win over Niagara, but St. John’s came out of the gate quickly against Syracuse and never lost control.

Point guard Federico Mussini scored 17 points, shooting 5-for-7 from three-point range, and Durand Johnson added 15. St. John’s got a huge lift off the bench from Amar Alibegovic and Kassoum Yakwe, who also had 15 each.

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Michael Gbinije topped Syracuse (7-3) with 21 points, but the Red Storm’s defense made things rough on outside shooters Malachi Richardson (15 points) and Trevor Cooney (11). Richardson shot 4-for-20, including 0-for-11 on three-pointers, and Cooney was 1-for-8 on threes. In addition, the Orange was outrebounded 51-36.

Shaking his head at the dramatic transformation, Mullin said, “With a young, inexperienced team, I don’t come in anticipating anything. You can’t because sometimes you draw everything up, and by the time I get to my seat, the ball is in the stands.”

On this day, the Red Storm kept the ball moving to find open shots and wound up with 22 assists. Alibegovic sparked an early 11-1 run with seven points for a 22-15 lead, and Mussini had nine in a 16-4 surge that pushed the lead to 40-29 just before halftime. In the second half, St. John’s never allowed the lead to drop below seven, pushing it to a high of 13 points at 71-58 on back-to-back threes by Alibegovic, who celebrated along with the roaring crowd.

“It’s been some time since I’ve played like this,” the sophomore forward said. “It was just all coming out at once. It was like pure adrenaline, and I was doing what I felt in the moment.’’

Mullin said Alibegovic’s hard work reflects progress made by the entire team. “We see it, but when you’re telling someone they can do it, it’s different when they go do it,” Mullin said. “Then they believe in themselves. The tipping point is when they go do it in a game. Then they prove to themselves.”

The Red Storm has reason to believe now.