Junior forward Brendan Crawford scored 15 and junior swingman Courtney Cubbage grabbed 12 rebounds for No. 7 Camden Catholic (12-6, 3-3).
"We'll learn from this," Irish coach Matt Crawford said. "We had some open looks, but they did a good job on defense."
The slow-paced game was played before a large crowd that included two chanting student sections.
With every possession at a premium, DaSilva's defense and some strong work on the boards by Cazan, junior Connor McLaughlin, and senior Sean Dumele made the difference for Bishop Eustace.
"For us, it all starts with our defense," Eustace coach Bob Falconiero said. "Flo is the key guy for us. He has to be disruptive but not cost us."
Falconiero said DaSilva has learned, through film study and coaching reinforcement, to limit his risks and stay in position.
Given his instincts, athletic ability, and reach, DaSilva still will have ample opportunity to make plays at the defensive end, his coach said.
"Some players, you game-plan for what they can do on offense," Matt Crawford said. "With [DaSilva], you always have to be aware of where he is on defense."
DaSilva made consecutive steals and turned them into baskets as Eustace rallied from an early deficit to take the lead midway through the second quarter.
Camden Catholic battled back behind Brendan Crawford, the coach's cousin, and the teams were tied at 17 at halftime.
But Bishop Eustace seized command of the game with a 13-2 edge in the third quarter. DaSilva had two assists and two steals in the decisive period.
"We knew they want to slow it down," DaSilva said. "We wanted to force a faster pace with our defense."
Bishop Eustace 3 14 13 11 – 41
Camden Catholic 6 11 2 14 – 33
BE: Flo DaSilva 9, Mike Cohen 10, Brandon Cazan 11, Connor McLaughlin 7, Sean Dumele 4.
CC: Rob Brosh 6, Tom Organ 2, Brendan Crawford 15, Courtney Cubbage 7, Jim Robinson 3.
Bishop Eustace's Flo DaSilva talks about the victory.