Fifth-seeded Lenape (20-6) moves to the sectional final Monday night against No. 3 Shawnee, which defeated Rancocas Valley.
"We've played in this game three years in a row, and we finally got over the hump," said Rob Hummel, in his third year coaching the Indians. "We were locking the other team up and playing really hard defense. And that's really been key to our success during this run."
Sears, a 6-foot-3 senior center, led all players with 17 points and 10 rebounds. She combined with 6-2 forward Maddie Sims (14 points, 11 rebounds) to dominate the boards.
"We just knew if we played great defense we would win the game," Sears said. "I'm just so proud of everyone on this team."
Lenape's lopsided advantage under the glass was a major factor in its allowing just four points over the first 15 minutes of the game.
The Indians played smothering man-to-man defense, grabbed nearly every rebound, and executed a methodical motion offense to jump out to a 26-4 second-quarter lead.
That gave them enough cushion to withstand a late Williamstown run.
"It was amazing to win this game. I don't even have words to describe it," Sims said. "We just stayed ready for any run that Williamstown made. We kept our cool and stayed focused."
Williamstown (17-10) chipped away at Lenape's lead throughout the third quarter, thanks largely to a full-court press.
Ciani Carter's three-pointer at the third-quarter buzzer made the score 36-27, marking the first time the margin was in single digits since the first quarter.
Lenape held on with patience and continued control of the lane on both ends.
"We had a great season," said Williamstown coach Karen Dilmore, whose Braves were fresh off an upset of top-seeded Washington Township in the quarterfinals. "We ran into a great team today. But this loss doesn't take away from what we've accomplished all season."
Williamstown 2 9 16 8 - 35
Lenape 15 11 10 10 - 46
W: Julia Dixon 4, Amber Anderson 5, Taylor Bynoe 15, Ciani Carter 11.
L: Taylour Jones 2, Alexis Sears 17, Rena Carabases 2, Alex Seedes 9, Mackenzi McErlean 2, Maddie Sims 14.