Senior guard Julian Martin added 14 points and five steals for top-seeded Williamstown (25-3), which will host seventh-seeded Shawnee in Monday's sectional finals. The Braves will make their first appearance in the South Jersey championship game.
Shawnee advanced Friday night by beating third-seeded Oakcrest.
Senior guard Brad Robertson scored 19 and senior center Will Kelly added 12 points with six rebounds and four blocks for fourth-seeded Lenape (23-6).
"I'm not sure anybody expected my kids to get this far," Lenape coach Chuck Guittar said. "It's a credit to them, to their hard work. I'm so proud of them."
Guittar said he blamed himself, not calling his final timeout with Lenape in possession with the score tied at 42 in the final minute. The Indians worked about 40 seconds off the clock but committed their 19th turnover with three seconds to play.
"I blew it," Guittar said. "I should have called a timeout. I'll second-guess myself for the rest of my life."
Williamstown coach Bill Hunt was worried about his team's ability to win in overtime. The Braves had survived the final 3 minutes, 12 seconds of regulation without 6-foot-6 senior Alssene Saintilus, who fouled out, and could have been hard-pressed to match up with the 6-8 Kelly through four minutes of overtime.
"I'm not sure what would have happened if we had to go four minutes [of overtime] without Alssene," Hunt said.
Williamstown called timeout with 2.2 seconds on the clock. Hunt designed a play to get the ball to D'Shawn Haines in the corner, with Hopkins as a second option.
"D'Shawn is our best outside shooter," Hunt said.
Haines was covered, so Julian Martin inbounded to Hopkins on the left side, just beyond the three-point line. With Lenape's Jeff Dinich playing tight defense, Hopkins dribbled to his right and released the ball just as the buzzer sounded.
"Curtis has hit so many big shots for us," Hunt said. "He stepped up big-time."
When the shot fell through the rim, Williamstown players and students rushed the court.
"They held me up," said Hopkins, who was in the middle of the wild celebration. "It was the same feeling I had as when I hit one [another game-winning shot] against Moorestown. But this was better."
Lenape 15 6 10 11 – 42
Williamstown 9 13 11 12 – 45
L: Jeff Dinich 5, Josh Nace 2, Brad Robertson 19, Will Kelly 12, Ben Cunningham 4.
W: Curtis Hopkins 16, Alssene Saintilus 8, Julian Martin 14, D'Shawn Haines 4, Marquis Little 3.
Contact staff writer Phil Anastasia at 856-779-3223