WILLIAMSBURG, 17 May 2015 (AFP) - France's Delacour, 21, finished at 11-under-par 202 and will aim for her first US LPGA Tour title in Sunday's final round.
"I think tomorrow I will be nervous," Delacour said. "It's my first time with the lead. But I'm going to try my best and we'll see after 18 holes."
Delacour, who has never led after any round on the LPGA Tour, is trying to join Patricia Meunier Lebouc, Anne Marie Palli and Catherine Lacoste as the only French winners on the LPGA Tour.
Second-round leader Lee, of the United States, dropped three strokes in two holes late in the round and fell into second place at 10-under at the Kingsmill Resort and Spa course.
The 20-year-old Lee made bogey on the par-four 16th then had a double bogey on the par-three 17th to post a one-under 70.
American Paula Creamer (66), South Korean Ryu So-Yeon (68) and Australia's Minjee Lee (69) share third place at nine-under-par 204.
Lexi Thompson is one stroke back at eight under after a 67.
Norway's Suzann Pettersen (69) is tied for seventh at seven-under 206. She was joined there by Kim Hyo-Joo (67), Angela Stanford (68) and China's Yan Jing (69).
Delacour had six pars and a birdie in her first seven holes. She then moved to nine under with a birdie at the par-four eighth.
After a pair of pars, she stumbled to a bogey at the 11th. Delacour made up for that wobble with a birdie at the 14th.
She birdied the 16th, then tapped in a short birdie at 18 to take the third-round lead.
Alison Lee saw her lead cut to two shots when she tripped to a bogey at the 16th. Her tee shot at 17 stopped on the fringe. She then four-putted for double-bogey that dropped her into a tie for the lead. She parred 18 to finish one back of Delacour.
Following Saturday's round, America's Lee was still agonizing over her late mistakes.
"I felt like I hit a couple decent strokes and I misread it," Lee said. "Especially on 15, 16 and 17, I hit strokes that I thought were good, but they didn't turn out as well.
"I'm pretty sure that four-putt on 17 will come back to haunt me tomorrow."
Leading third-round scores on Saturday in the US LPGA Kingsmill Championship (USA unless noted, par-71):
202 - Perrine Delacour (FRA) 67-68-67
203 - Alison Lee 66-67-70
204 - Paula Creamer 67-71-66, Ryu So-Yeon (KOR) 67-69-68, Lee Min-Jee (AUS) 68-67-69
205 - Lexi Thompson 72-66-67
206 - Kim Hyo-Joo (KOR) 70-69-67, Angela Stanford 68-70-68, Suzann Pettersen (NOR) 72-65-69, Yan Jing (CHN) 70-67-69
207 - Kelly Tan 74-69-64
208 - Hur Mi-Jung (KOR) 68-73-67, Ryann O'Toole 70-71-67, Kris Tamulis 70-70-68, Julieta Granada (PAR) 72-66-70
209 - Maria McBride 71-69-69, Mariajo Uribe (COL) 68-71-70, Park In-Bee (KOR) 72-67-70, Christina Kim 69-68-72