It was almost as if Plymouth Whitemarsh purposely played into the hands of Lower Merion in the first half of Friday night's PIAA District 1 Class AAAA boys' basketball quarterfinal.

The hosts allowed the Aces to slow the pace down to a crawl. They notched several uncontested layups while spreading the floor, and Lower Merion confidently built an 11-point advantage before a standing-room-only crowd at Colonial Elementary School.

"We let them walk the ball up the court and settle into their half-court sets," Colonials coach Jim Donofrio said. "We needed to be more aggressive and take risks."

PW flipped the switch midway through the third quarter, put together an incredible 25-3 run, and advanced to the semifinals for the first time since 2011 with a thrilling 47-36 triumph.

"They sat out there in the first half, held the ball, did what they wanted," Colonials senior guard Jimmy Murray said. "We were able to push them into our traps in the second half. That was the difference."

PW's only second-quarter score came on Xzavier Malone's three-point play with 4.8 seconds left until intermission. Lower Merion was ahead by 19-11 at the break and by 27-20 in the third period.

"We played a little soft in the first half," said Malone, a junior guard and Martin Luther King transfer. "At halftime, Coach 'D' said to us, 'We're not losing at home like this. We're going to Temple.' "

The No. 4-seeded Colonials (23-2) will take on No. 9 Ridley, a 36-34 upset winner Friday over No. 1 Conestoga, in a semifinal at 7:30 p.m. Wednesday at Temple's Liacouras Center.

The No. 12 Aces, who committed 16 of their 23 turnovers in the second half, will visit Conestoga, a rival in the Central League, in a playback contest.

Malone (15), Andre Mitchell (13), and Murray (11 second-half points) combined for 39 points. Forwards Devon Monteiro-Gray (six points, six rebounds) and Cameron Johnson (seven rebounds, two steals, and two assists) also played key roles.

"It was our defensive intensity that turned things around," Murray said. "Coach 'D' emphasizes it: defense, defense, defense."

Steve Pendleton paced Lower Merion (16-10) with 15 points and nine rebounds. Backcourt mate and fellow senior Corey Sherman hit a pair of treys on the way to nine points.

Lower Merion 8 11 8 9 - 36

Plym.Whitemarsh 8 3 20 16 - 47

LM: Steve Pendleton 15, Corey Sherman 9, Jule Brown 6, K.J. Helton 4, Eli Needle 2.

PW: Andre Mitchell 13, Jimmy Murray 11, Devon Monteiro-Gray 6, Cameron Johnson 2, Xzavier Malone 15.