Mt. Vernon senior Audrey LaSalle buried three quick treys to push the Lady Mountaineers to a quick 11-0 lead.
Jayse Henderson's 3-pointer with 3:00 minutes remaining in the first period erased the goose egg on Purdy's side of the scoreboard. After one period the visitors led 20-7.
"There is no excuse for the way we played to night," said Purdy coach Eli Ernst. "Mt. Vernon didn't do anything different than what our scouting reports said. We just failed to execute our game plan."
Mt. Vernon didn't help matters by connecting on five of their first six attempts from downtown. By the intermission the green and white had sunk seven 3-pointers and amassed a 40-15 lead.
"We are going to learn and get better from tonight," said Ernst. "We have got to settle into the game quicker."
Purdy trailed 53-29 after three periods and were outscored 15-8 in the final frame.
Scoring for Mt. Vernon: Henderson, 21 points; LaSalle, 16; Mackenzie Farmer, 11; Laynie Dake, 9; Megan Pope, 7; and Karlie Meeks and Payton Woodrum, 2.
Scoring for Purdy: Mattie White, 10 points; Billie House, 9; Jayse Henderson and Courtney White, 5 apiece; Desirie Ennes and Andrea Humphrey, 3 each; and Katie Hughes, 2.