The leaders are tied on five-under-par 283 after four rounds, including two rounds on the North and South Courses respectively. They are one stroke ahead of England's Charlotte Thomas.
All the action will come to a climax in Sunday's final round, to be played over the South Course, after which the top five players will earn LET Membership in Category 5c, offering entrance into virtually all of the 24 tournaments on the 2020 LET schedule and access to the €18 million prize money. Players from the 6th to the 20th position will be eligible for Membership in Category 8a.
After a tough third round of 77 on the North Course, co-leader Muirhead was delighted to bounce back with a bogey-free three-under-par round of 70 on the South.
The 21-year-old Dubai-based Scot said: “It was really steady today and I enjoyed it. The conditions altered during the round so it was good to keep it steady and hit a lot of greens. I just kept lipping out for birdie, so it was very nice to see the ball rolling close today and to bounce back, especially after yesterday. I’m very pleased.
“I’m feeling really good heading into tomorrow. It’s obviously another day, but I feel like my putter is working well. I didn’t hole as many putts today, but you obviously save them for the next day, so I’m really looking forward to tomorrow.”
Boulden, the 2014 Rookie of the Year, is looking to regain her LET card after a year on the Symetra Tour. The 26-year-old from Llandudno moved into a share of the lead with a brilliant four-under 67 on the North Course, where she also shot 67 in the second round.
The best round of the day belonged to Thomas, who shot a five-under-par 68 on the South Course.
Rachel Drummond, whose round included a hole-in-one on the South Course’s 12th hole, made the cut on the number and was one of 65 players at 10-over-par or better to advance to the final round.