Given the departure of Georgetown’s top three scorers, the points weren’t expected to come easily for the young Hoyas in the early going this season.

But their offensive challenge got even tougher just six minutes into Sunday’s game against Duquesne when sophomore Otto Porter Jr. was sent to the locker room after getting hit in the head during contact under the basket and was held out the remainder of the game as a precaution.

Porter’s injury created an opening for freshman D’Vauntes Smith-Rivera to prove his mettle. And on a night when the Hoyas’ unfamiliarity with their offense was glaring, he proved himself invaluable, scoring a team-high 19 points on 6-of-7 shooting to pace Georgetown to a 61-55 victory.

The 6-foot-3, 227-pound Smith-Rivera, the most highly touted among a five-man freshman class, hit every shot he attempted in the first half, including four three-pointers and a would-be fifth that swished through the net just after the buzzer sounded.

Coach John Thompson III didn’t put a timetable on Porter’s return, saying, “We’re just going to monitor him the next few days and see.”

Sophomore forward Mikael Hopkins was the only Hoya to join Smith-Rivera in double figures, finishing with 13, while Greg Whittington grabbed a game-high 15 rebounds, including a crucial one with 28 seconds remaining after Duquesne had pared an 11-point deficit to three.

When Jabril Trawick’s free-throw attempt thudded against the backboard, the 6-8 Whittington leapt for the rebound and, in the process, earned his own trip to the stripe and hit both attempts.

“That was a crushing blow right there,” said Duquesne Coach Jim Ferry, who summed up the contest as “early, ugly basketball from two inexperienced teams.”

Thompson concurred.

“I think both teams were sloppy,” Thompson said. “We definitely were sloppy at both ends of the court. It’s early.”

It was Georgetown’s second shot at a first game. Friday’s contest against No. 10 Florida aboard the USS Bataan was scuttled at halftime after temperatures dipped and heavy condensation rendered the floor a hazardous puddle of water. Florida led 27-23 at the break, and Thompson said afterward that he wanted his team to do a better job penetrating had play resumed.

The theme remained the same against Duquesne, which is also in a rebuilding mode and starts a freshman point guard, 5-11 Derrick Colter of Forestville.

A crowd of 8,213 turned out for the home opener at Verizon Center. The Hoyas started four players 6-8 or taller; Duquesne, none. Nonetheless, the Hoyas struggled to get the ball inside and couldn’t get much to fall from the perimeter, while Duquesne bolted to an 8-3 lead.

Smith-Rivera came in for junior Markel Starks roughly five minutes into the game and knotted the score with a three-pointer, then struck again from long range to put Georgetown ahead.

The Hoyas made just one of their first five free throws, turned the ball over and rushed an uncharacteristic number of shots.

Smith-Rivera was the exception, converting every clear look at the basket to pace a 27-21 lead at the break.

“We were forcing too much — hunting for our points instead of making the ball move,” Thompson said.

When Porter didn’t return for the second half, Smith-Rivera assumed his spot in the lineup.

Duquesne pulled within 29-28, but Starks (nine points, one assist) snapped an 0-for-4 shooting drought on a fast break.

The Hoyas’ 6-9, 250-pound Moses Ayegba entered the game with just over 15 minutes remaining, Georgetown leading 33-28, and got two rebounds in three minutes of work.

Whittington gave Georgetown its first double-digit lead from the free throw line with 9 minutes 23 seconds to play. But the Dukes kept scrapping.

Sunday’s opener was a regional round game of the Legends Classic, which pits the Hoyas against Liberty Wednesday at Verizon Center and takes them to New York’s Barclays Center Nov. 19 and 20, when they’ll face UCLA and either Indiana or Georgia.