Sean Crocker chipped in for an eagle on the par five 18th hole to give him a two-stroke lead going into the final round at the Hero Open.
The American, bidding for his first European tour title, finished on a 3-under 69 on Saturday to keep Jens Dantorp of Sweden two shots behind after three rounds at St Andrews.
Crocker, who started the day with a one-shot lead, moved to 18 under for the tournament as he goes for a wire-to-wire win.
"That was a nice little bonus on 18. I was trying to get it up and down for (birdie) but to see that ball drop was pretty cool," said Crocker, who was born in Zimbabwe and raised in California.
He ran into trouble on the par four 13th when he was in the thick rough after two shots and near a wall. He took a drop and settled for a double bogey.
He had thought about playing it, though.
"Every time I got near that ball I just could see bad things happening," he said. "We made the right decision there by taking the drop."
Dantorp is alone in second after a bogey-free 69.
Adrian Otaegui (64) and David Law (65) are both three shots off the lead.
"It's nice to have a little bit of room but I also know those gaps can be closed very quickly," Crocker said. "It's been a long time since I've held something shiny. It would be a nice little present."
Daniel Hillier, of New Zealand, is six shots behind Crocker on 12 under. Australia's Dimi Papadatos is eight under, Ryan Fox, of New Zealand, is seven under and his compatriot Josh Geary is five under.