Zack finished with a career-high 19 points and matched a personal best with eight rebounds in 38 minutes to pace the Explorers, who saw four players reach double figures. Nine of Zack's points came in the final four minutes.
"I thought he clearly was our most improved player in the offseason," Giannini said. "This time last year I tried to explain to people, talked forever about the difficulty big post players have adjusting to college basketball.
"He learned and he's tough. He's worked and is motivated. Most importantly, he got in great shape. Not many guys his size are in the kind of shape he's in. He's really improved. I expected him to improve but he made a big jump."
Zack's play was a tremendous sign for Giannini, who knows his team's strength is with the backcourt combination of Tyreek Duren, Ramon Galloway and Sam Mills. And the Explorers are eagerly awaiting the eligibility of another guard, transfer Ty Garland (Virginia Tech), who is the third all-time leading scorer in Philadelphia Public League history, after the first semester.
Duren, the point guard, was steady against the Hens, with 12 points and one turnover. Galloway (seven points), playing with an injured hip suffered in practice last week, and Mills (10 points) were good but likely will be relied upon for more if La Salle is going to succeed.
"The strength of our team will continue to be our guards," Giannini said. "When you know what our guards can do, you know we're going to play better than that. I'm thrilled at every level."
Duren made a pointed effort to get the ball to Zack down the stretch.
"Most times when Zack is in the post he has an advantage," Duren said. "I told him (after La Salle's exhibition game Nov. 2) next time we play, look to score. He came out real aggressive and he was successful with it. We have a real complete team."
Jarvis Threatt had 17 points to lead Delaware.
La Salle, which led 38-32 at the half, was up five after a Mills three-pointer made it 48-43 with 15:27 remaining. But things got tight after that.
Devon Saddler scored 10 straight points over more than seven minutes, as the teams traded one-point leads for several minutes. Delaware took its final lead with 5:58 left on Saddler's jumper that made it 57-56.
Then Zack took over.
The native of New Cumberland, Pa., netted seven of the next nine Explorers points to give the home team a five-point cushion, 65-60, with 2:59 remaining. That would be enough of a cushion.
"I'm coming back new and finding a comfort zone," Zack said.
Jamelle Hagins scored with 1:43 left to make it 65-62 before a pair of Galloway free throws pushed the home team's advantage back to five with 52.8 ticks left.
The Explorers are coming off their most successful season in two decades when they went 21-13 and lost in the first round of the NIT, snapping a 20-year postseason drought.
La Salle, which was picked to finish seventh in the deep and talented Atlantic 10, is vying for its first NCAA tournament berth since 1992. The Explorers return most of their key pieces from last season.
The Explorers put their talented backcourt on display in the opening 20 minutes when they took a 38-32 lead. La Salle led by as many as 15 points, but the feisty Blue Hens hung tight. Duren had 10 points in the opening 20 minutes for the Explorers, who shot 13-for-33 (39.4 percent) from the field.
Delaware, picked second in the Colonial Athletic Association behind Drexel, is coached by former St. Joseph's assistant Monte Ross.