Up 54-27 midway through the third quarter after Jahaire Wilson's acrobatic putback and free throw after a foul, the fun was over.
Just turnovers and missed shots -- which Bearcats coach Troy Sowers called rushed -- and 14th-seeded Hempfield (13-10) steadily pulled closer to third-seeded William Penn (24-2).
"They made shots. I thought their 3s were contested," Sowers said. "We were flying to almost all of those 3s, and they made them.
"I'm glad that we got a little cushion in the first half where we could stave off a little rally."
He drove at the hoop and stepped back to fire from deep. Even with that offensive effort and Hempfield's 16-point run, William Penn's lead was still double digits. The Knights never got closer than eight, as Parker's jump shots that fell early started to connect again.
By the time he and his Bearcat teammates finished, Parker had a game-high 32 points needed to avoid an upset at home.
"We have to learn how to nurse a lead better," he said. "They came out and hit a couple of shots, and we rushed a couple of shots like we were down.
"We need games like this. As a player you like to win and learn along with the wins."
For 18 straight games, that's what they've done. William Penn will take that winning streak into Giant Center on Saturday morning against sixth-seeded Chambersburg, a 40-37 winner against Cedar Crest on Wednesday. The night saw the district's top two seeds, Harrisburg and J.P. McCaskey, win by at least 26 points in their tournament openers.
The Bearcats looked to do the same.
Their lead on Hempfield grew to 20 when Derek Wilson's dunk in the final three minutes of the first half stamped his return. Wilson, who rolled his right ankle in practice last Thursday before the Bearcats' YAIAA title win against South Western, didn't play in that game except for the final seconds to see the floor.
The leaping senior forward gingerly strolled back in transition after his dunk. Sowers said his second-leading scorer is at about 75 percent.
"This was a whole lot of effort for the limited stuff he's done for the last five days," said Sowers, who limited Wilson to shooting around at practice.
While Sowers said Wilson "looked a little rusty, and that's to be expected," so was the vigorous play of the younger Wilson and 5-foot-10 junior guard Stephen Dickson. The two were responsible for every William Penn rebound until sixth man Ramel Stephens began a short parade of putbacks nearly two minutes into the second quarter. It was continued on the next possession by Jahaire Wilson.
"That's always big, rebounding, because it gives us second chances at the basket," Parker said, "and Jahaire was a man down low."
The effort helped William Penn to a 37-26 rebounding advantage. Dickson had seven of them.
"As a team, we push each other at practice, and we know what it takes to win is you have to do it all," he said. "You can't just have, set in stone, one person's going to score and one person's going to do this and that. We just all try to get after it."
Bleacher 2 0-0 4, Tyrell Wickersham 7 5-6 23, Drew Johnson 5 6-8 18, Zach Walter 3 3-4 11, Criswell 0 4-6 4, Corso 1 0-0 2, Stuckey 0 0-0 0, Green 1 2-2 4, Burke 0 0-0 0. Totals 19 20-26 66.
WILLIAM PENN (74)
Dickson 2 0-0 4, Casiano 1 3-4 5, Tavon Parker 11 7-11 32, Derek Wilson 5 1-2 11, Jahaire Wilson 5 2-2 12, Ramel Stephens 3 4-5 10, Shifflett 0 0-1 0, Jackson 0 0-0 0, Rivera 0 0-0 0, Maddox 0 0-0 0. Totals 27 17-25 74.
Hempfield 10 11 19 26 -- 66
William Penn 18 25 11 20 -- 74
3-point goals -- Hempfield 8 (Wickersham 4, Johnson 2, Walter 2); William Penn 3 (Parker 3).