Jerian Grant of Notre Dame shoots the ball against Jabril Trawick of Georgetown. The Irish finished with their lowest point-total at home since 1972. (Michael Hickey/GETTY IMAGES)

After muzzling the Big East’s sharpest-shooting team through the first half, Georgetown let a15-point lead get slashed to three in the fever-pitched confines of the Joyce Center, where Notre Dame had won 47 of its previous 49 games.

With 12 minutes yet to play, it seemed likely that the Hoyas would buckle as they had two nights earlier against the struggling South Florida Bulls.

But reserve Moses Ayegba grabbed a key offensive rebound. And with an assist from Otto Porter Jr., freshman D’Vauntes Smith-Rivera drilled a three-pointer that declared the rout back on. With it, Georgetown rolled to a 63-47 victory that scrambled all notions of just who these young Hoyas are and what they’re capable of.

Georgetown (13-4, 3-3 Big East) held the 24th-ranked Fighting Irish to their fewest points in a home game since 1972 (a 57-32 loss to UCLA) by denying attempts from the three-point line and contesting shots lofted from all corners of the court. The Irish, whose 49-percent shooting entering the game leads the Big East, made just six field goals in the first half and 17 of 49 overall.

Led once again by sophomore forward Otto Porter Jr. (19 points, nine rebounds), Georgetown didn’t simply bounce back from its listless defeat at South Florida. The Hoyas reinvented themselves, getting significant contributions from reserves such as Smith-Rivera, who scored 10 of his 14 points in the second half, and Ayegba, who ably held down the front court after Nate Lubick drew his fourth foul.

None of Ayegba’s season-high 10 rebounds was more important than the one he grabbed once the Irish pulled within a basket.

“That was really the turning point of the game,” said Notre Dame’s senior forward Jack Cooley, held to 10 points on 4-of-11 shooting. “If we would have gotten that rebound, who knows what would have happened.”

Instead, Porter and Smith-Rivera, an Indianapolis native who had numerous relatives in the stands, erupted for 15 consecutive points between them.

Notre Dame Coach Mike Brey didn’t call a time out until the Hoyas’ scoring run reached 18-0. By then, the crowd had fallen silent, and famously loyal Irish fans headed for the exit with Georgetown leading 58-37 and just less than five minutes to play.

“That’s a terrific offensive team; a terrific team overall,” Georgetown Coach John Thompson III said of Notre Dame. “For a very good offensive team, for the most part we made things difficult for them.”

With snow gusting from Lake Michigan, forecasters said the 10-degree temperature felt like minus-4 shortly before tip-off. The frigid weather and slippery roads didn’t keep Notre Dame fans from piling into Joyce Center.

But the visitors seized the momentum early, bolting to a 21-8 lead.

Once Brey demanded more defensive attention to Porter, the Irish pulled within four, 25-21. But the Hoyas kept battling on defense. Markel Starks (nine points, five rebounds, four assists) hit a jumper with 3 minutes 36 seconds remaining in the period. Smith-Rivera scored quickly off a Notre Dame miss.

And after a series of empty possessions by the Irish, a clutch jumper by Starks restored the double-digit lead. Porter hit just before the clock expired to give Georgetown a 34-21 lead at the break.

Notre Dame (15-4, 3-3) shot just 30 percent in the period.

“Hey Brey! Play your bench!” an unhappy Notre Dame fan shouted.

The arena erupted when Pat Connaughton drilled a three-pointer for the Irish. In a flash, Georgetown’s lead was slashed to three, 40-37.

With Lubick relegated to the bench upon drawing a fourth foul, the Hoyas’ front court was thinning. That’s when Porter and Smith-Rivera keyed the 18-0 run.

“I definitely wanted to perform well in front of my family,” Smith-Rivera said.