Ben Martin shot a third-round 62 to take a two-shot lead at the Shriners Hospitals for Children Open.
The American carded 10 birdies, including five in a row from the 13th, against a solitary bogey to move on to 17 under for the tournament.
Scotland's Russell Knox, the joint overnight leader, remained in contention with a five-under 66 to sit second overall at 15 under.
Knox fired five birdies in a flawless round to go into the final day two shots clear of Americans Jimmy Walker, who also went round in 62, and Andrew Svoboda.
Walker's bogey-free round featured nine birdies, while Svoboda's eventful 67 included six birdies, four bogeys and an eagle three at the 13th.
A group of four more American players were a shot further back on 12 under; Brooks Koepka, Kevin Streelman, Scott Piercy and 2012 US Open champion Webb Simpson.
Keeping it simple
Martin, 27, who is seeking his first PGA Tour title, insists he is determined not to overcomplicate the task at hand.
"Just go out tomorrow with the same mindset, head down, and try to keep making birdies," he told the PGA Tour website.
He also spoke about how he knew from the very first hole he was going to have a good day on Saturday, adding: "I felt it from the first hole (when) I made a 20-footer for birdie.
"So I felt confident with my putter and I was getting a lot of looks. I've played that stretch of holes well all week, 15 and 16, and that's really the part of the course that most guys are making their birdies."
Knox, meanwhile, was satisfied with his efforts as he remains within striking distance going into the final round.
"Bogey-free on a Saturday is exactly what I wanted," said the 29-year-old Scot. "I knew I was going to make birdies and I'm seeing the lines on the greens really well. I knew if I just limited my mistakes, I was going to be right up there."