Wendy Ward and Se Ri Pak each posted rounds of 3-under 69 to move into a tie for second place at 9-under-par 207. Annika Sorenstam is one stroke behind that duo at minus-8, while defending champion Karrie Webb is alone in fifth at 7-under-par 209.
Meunier-Lebouc, the winner of the season's first major at the Kraft Nabisco Championship, began her round at Royal Lytham & St. Annes Golf Club three strokes behind overnight leader Heather Bowie. Meunier-Lebouc quickly burst out of the gate with birdies at each of the first two holes.
The Frenchwoman had her momentum halted when she bogeyed the third hole but she quickly recovered. She sank a nine-foot birdie putt at the fourth and followed that with another nine-footer for birdie at the next.
The 30-year-old then bombed a 3-wood within five feet of the cup for an eagle at the par-5 sixth to climb to 10-under for the tournament. She missed the green at the next and bogeyed the hole to drop back to minus-9.
Meunier-Lebouc ran off nine straight pars before birdieing the 17th to move into a three-way tie for the lead. However, late bogeys by Ward and Pak gave Meunier-Lebouc the advantage after 54 holes.
'The big difference today was the putting,' said Meunier-Lebouc. 'I really putted much better than the other days. Today, I started great and finished good. It was very tough to keep relaxed all the way. I just managed to stay calm, make pars and then that great putt on 17 was back to the good putting again.'
If Meunier-Lebouc wins this week, she will be the first player since Webb to win two majors in a season. Webb accomplished that feat in 2000 and again in 2001.
'Today, it was tough at the end to stay calm and relaxed,' Meunier-Lebouc said. 'It's also because it's the British Open, the conditions are very different than any other major. I think with the wind, it's the only conditions that I've been in that's been tough for me to play, but I've really improved outside of my game.'
Pak's late struggles cost her the overnight lead. She had three birdies on the front-nine to move to minus-9. Around the turn, birdies at the 11th and 13th moved her to 11-under and solo first place.
The South Korean bogeyed No. 14 but recovered that shot with a birdie at the 16th. She stumbled down the stretch though with back-to-back bogeys to close out her round.
'I feel great. It's not the way I wanted to finish, on 17 and 18, but that is golf here,' said Pak. 'This golf course has so many troubles out there, but I did really well. I'm really happy with my game and I think in great position for the final round.'
Ward got off to a good start as well with birdies at the second and fourth to get to 8-under.
Around the turn, she caught fire with back-to-back birdies from the 10th to climb to minus-10. However, she bogeyed the last to fall back into a share of second place.
'I played really solid,' said Ward. 'I probably hit the ball the best of any of the three days here this week, and so it's kind of frustrating, ending with a bogey and having nine-iron in your hands and missing the green. But I just got a little aggressive with my approach and came over the top of it a little bit. Hopefully I won't make that mistake tomorrow.'
Sorenstam, who is looking to complete the career grand slam, eagled the par-5 sixth to get to minus-6. Birdies at the ninth and 11th moved her into fourth place.
Webb bogeyed the second hole but recovered with three birdies over the final 16 holes to stay in contention.
Bowie struggled to a 2-over 74. She shares sixth place with Grace Park at 6-under-par 210. Kelli Kuehne and Paula Marti are one stroke further back at minus-5.
Beth Daniel and Vicki Goetze-Ackerman share 10th place at 4-under-par 212. Candie Kung, Sophie Gustafson, Karen Stupples and Becky Morgan are one behind that duo at minus-3.
Lorena Ochoa and Akiko Fukushima, who shared fourth place entering the round, both had big problems on Saturday. Fukushima had two bogeys and two birdies on the front nine but she opened the back nine with a triple-bogey and followed that with a double-bogey at the 10th. She posted three more bogeys and a birdie on her way to a 7-over 79.
Ochoa had four birdies and three bogeys in her round, but it was the par-3 12th that did her in. She carded a nine on the hole and that dropped her from minus-5 to plus-1 at the time. She finished with a 5-over 77.