Clement Sordet of France produced an unblemished 9-under-par 63 to steal the lead from Jamie Donaldson of Wales by two strokes after the third round of the Thailand Golf Championship on Saturday.
Sordet made seven birdies and eagled the par-5 15th hole for the outright lead, his first on the Asian Tour. Sordet turned pro this year after graduating from university in the United States, and usually competes on the European Tour's second-tier Challenge Tour.
"I just stayed patient, but honestly I had no idea I was 9-under at the end," he said. "So, 9-under, I'm pretty happy about it."
Donaldson, leading since the opening round, began the day with a two-shot lead but fell two behind and clung on to second place.
He mixed in six birdies, three bogeys, and a double bogey on the par-4 12th to submit a 1-under 71 and a three-day total of 14-under 202.
"I was cruising. Playing not great but doing enough until 12, which was a killer," Donaldson said. "Tomorrow's another day, and I just have to get off to a quick start. I've done enough to stay in the tournament - I'm still in it."
Defending champion Lee Westwood was in contention for a third title at Amata Spring Country Club after carding 64 to be 13 under for the tournament, three off the lead. He was alone in third place.
"I was confident and in control, and it has got to do with being on a course which I've won twice before," Westwood said. "I hit it close a lot, and I played with a new putter. It feels a lot more stable, and I'm rolling the ball quite nicely with it."
Another stroke behind in fourth was European Tour rookie of the year Byeong-hun An of South Korea (68).
Tied for fifth, five shots off the pace, were 2013 champion Sergio Garcia (70), and last year's runner-up, Martin Kaymer (72).