South African Pace and Frenchwoman Herbin hold a two-stroke lead over Sweden's Mikaela Parmlid going into the final round at the Club de Campo Villa de Madrid.
Parmlid moved up four places to claim third on her own thanks to a fine 66 to ensure she will play with the leading duo.
Herbin had looked set to be the outright leader until a bogey on the 17th dropped her into a tie with Pace, and they both parred the final hole.
A third successive 68 from Herbin, which included five birdies, had been blemish-free until she slipped up on the 17th.
Herbin, whose caddie is Seve Ballesteros' brother Vicente, told the Ladies European Tour website: "I'm very happy and very warm, because it was a long day, but I'm happy with my game.
"I hit 16 greens and had five birdies again, so just a little mistake, one bogey: a three putt, but generally I'm very happy with my putting. It's getting better and better every day."
Pace, a six-time tournament winner on the Ladies European Tour, had a bogey-free 68, with her four birdies on the front nine.
"My consistency is one of my strong points and I don't make a lot of mistakes," she said.
"If I do, it's not a big mistake and I let the putts fall. I was okay in the beginning but seemed to lose concentration towards the end. I still played well and happy with where I am."
Parmlid, who had a flawless 66 containing six birdies, said: "I hit the ball better today [Saturday] and had a really good start, with four birdies in a row. I felt calm.
"I think it was much hotter today [Saturday] and on 16 I had to pour water on my head to cool down."
Carlota Ciganda leads the home challenge after the Spaniard posted her own 66 to lie in a three-way share of eighth place, seven shots off the lead.