"I put a lot of emphasis on making sure we got off to a good start," Dempsey said. "Everybody knows if you get down against Lower Merion, they're going to spread you out, go four corners, and get what they want."
The Explorers, who will face Chester in a Tuesday semifinal at a neutral site and a time to be announced Sunday, won the overall rebounding battle, 39-19. The stunned Aces collected only three offensive caroms.
"They played great, and we played bad," Lower Merion senior Justin McFadden said. "They went out and really executed their game plan."
Senior forward Jalen Herdsman and junior guard Shawn Witherspoon paced La Salle (22-6) with 14 points apiece.
The 6-foot-5, 190-pound Herdsman, who gathered 11 boards, provided eight third-quarter points. His three-point play, off a terrific feed from junior point guard Najee Walls, made it 51-31 entering the final period.
"The coaches stressed that we needed to come out strong and fast," said Herdsman, who is considering Gwynedd Mercy for college. "That's what we did."
The Explorers received strong bench play from Sean Greenberg (nine points, four rebounds, two assists, two steals), Shane Stark (six points, three rebounds), and Dan Corr (four points, two assists),
Witherspoon totaled six rebounds and two assists; Walls scored all 13 of his points in the second half; and Dave Krmpotich, a 6-foot-7 junior, chipped in six rebounds and five points.
Of his team's 21-point cushion at the break, Dempsey said, "We told the kids to treat it as if the score was 0-0. We wanted to still be relatively aggressive."
McFadden, a Binghamton recruit, and junior forward Jule Brown each scored 16 points for the Aces. Lower Merion (23-8) shot 2 for 18 (0 for 10 in the first half) from three-point range.
La Salle 15 18 18 20 - 71
Lower Merion 5 7 19 17 - 48
LS: Najee Walls 13, Chuck Champion 4, Dave Krmpotich 5, Jalen Herdsman 14, Shawn Witherspoon 14, Sean Greenberg 9, Dan Corr 4, Shane Stark 6, Mick Barrett 2.
LM: JaQuan Johnson 11, Corey Sherman 1, Jule Brown 16, Justin McFadden 16, Steve Pendleton 2, K.J. Helton 2.