Junior guard Dayshawn Reynolds scored 13 and senior forward Keyshawn Reynolds, his cousin, added 12 for Atlantic City (3-3, 3-1).
"Give Sommers credit - he knocked them down," Atlantic City coach Gene Allen said of Sommers' fourth-period foul shooting.
Sommers said he waited his whole career to play a game such as this one - big crowd, back-and-forth game against a fierce rival.
"This was huge for me to play in this game after working so hard to get here," said Sommers, who lives in Galloway Township.
Sommers played a lot of minutes in the first three quarters but scored just one point.
"I think I must have missed four three-pointers," Sommers said. "I was trying not to get frustrated."
Holy Spirit weathered an Atlantic City surge in the second quarter, as the Vikings went on a 10-0 run to take a 19-11 lead. The Spartans also survived the final 7 minutes, 46 seconds of the third quarter without Moore, who sat out because of four fouls.
"I can't tell you how proud I am of these kids," Holy Spirit coach Jamie Gillespie said. "There were five different chances for us to lose this game, and these kids just refused to lose. They were absolutely exhausted, but they refused to lose."
Atlantic City was just 10 for 21 from the foul line.
"Really, the game came down to free throws," Allen said. "That hurt us, and they knocked them down."
Saintel, a rangy, 6-foot-5 athlete who is one of the top sophomores in South Jersey, made a series of plays in the third quarter to help the Spartans survive in Moore's absence.
"I was nervous, but I knew I needed to help my team," Saintel said.
Sommers was 6 for 8 from the foul line in the fourth quarter and also hit a three-point jumper that rattled around the rim before falling through the net.
"I was having a heart attack," Sommers said. "To hit that three, in this type of game, that was great."
The victory gave the Spartans sole possession of the American Division lead, although they still must travel to Atlantic City to play their fiercest rivals in the rematch.
"It was a huge game for us," Sommer said. "This puts us in great shape in the division, and beating Atlantic City is always big for us."
Atlantic City 12 11 10 19 – 52
Holy Spirit 11 13 13 19 – 56
AC: Martel Johnson 2, Dayshawn Reynolds 13, Ahmed McKinley 9, Kashaun Dunston 10, Quashaun Dorn 2, Dennis White 4, Keyshawn Reynolds 12.
HS: Paul Moore 16, Larry Jones 11, John Sommers 10, Junior Saintel 12, Uuhmad Collier 2, Mark Rassman 5.
Contact staff writer Phil Anastasia at 856-779-3223, panastasia@phillynews.com, or @PhilAnastasia on Twitter. Read his blog, "Jersey Side Sports," at www.philly.com/jerseysidesports
