Sean Dixon hit a pair of layups as Williamsport closed with the last seven points of the period. The rally continued as Greg Minnick's basket with 1:27 left in the half tied it at 20-20.
Minnick stole the ball from Brunswick guard Marcus Hall and turned it into an old-fashioned three-point play with 1.9 seconds left to give Williamsport its first lead at 23-22.
"It just spiraled out of control," said Brunswick coach Dan McLane. "We started well, then stopped making shots. We missed a bunch of easy looks and even when we got fouled, we weren't able to hit free throws.
"Then they get a turnover and basket at halftime and get the momentum."
Minnick finished with 21 points and 12 rebounds, while Dixon scored 13 and Eric Wilfong and A.J. Jamison each had nine points. Wilfong saw some action at point guard and dished out six assists, while hauling in seven rebounds.
The Wildcats began pulling away in the third quarter as Dixon's putback with 55 seconds left made it 37-27. A three-point play by Jamison extended the lead to 50-36 with 4:20 remaining.
Brunswick had one last hurrah left, as it reeled off nine straight points to close the deficit to 50-45 with 1:44 left.
"It's the same old story. We get off to a slow start and then get a fire under our belly and start to play well," Mowbray said. "But when it's time to deliver the knockout punch, we can't do it. After the timeout, we got it together."
The Wildcats regrouped and nailed their last eight free throws to clinch the win and sole possession of first place.
After the hot start, Brunswick finished the game 13-for-47 from the field (27.6 percent). Andrew Simpson led the Railraoders with 19 points despite being held scoreless in the final 6:44. Hall added eight points and Justin Stone had 13 rebounds.
Brunswick could possibly have a third shot at the Wildcats when the Maryland Class 1A West playoffs begin next week. They must win two games to reach the semifinals, where a potential trip to top-seeded Williamsport looms.