Christiaan Bezuidenhout extended his lead to five shots heading into the final round of the Andalucia Masters but home favourite Jon Rahm played his way into contention on day three at Valderrama.
South African Bezuidenhout carded a battling 69 to get to 10 under on one of Europe's most feared layouts as he looks for a first victory on the European Tour.
Ryder Cup star Rahm has six solo wins to his name worldwide and he finally seemed to get to grips with a course where he has struggled in the past, matching the lowest round of the day with a 67 to share second place alongside Japan's Hideto Tanihara.
Rahm turned in 32 with birdies on the fourth, sixth and eighth and then recovered from a bogey on the 15th with a birdie-birdie finish to set the clubhouse target.
Bezuidenhout was four ahead at that point after a single birdie on the second and he sandwiched a bogey on the 14th with further gains on the tenth and 16th to stretch his advantage.
"Going into Sunday with a five shot lead is definitely nice," he said. "Rahm is a great player, he's top 15 in the world and he's a legend in Spain so it will be quite an experience tomorrow."
Tanihara carded a 68 to sit two shots ahead of Belgian pair Nicolas Colsaerts and Thomas Detry, with tournament host Sergio Garcia and England's Steven Brown in the group eight shots off the lead.