Playa del Carmen - Unheralded Derek Fathauer fired a second straight 66 on Saturday to take a one-shot lead into the final round of the OHL Classic at Mayakoba.
Fathauer, trying to become the sixth straight first-time winner on the US PGA Tour, had a 16-under total of 197, one shot clear of veteran Jason Bohn, who carded a 65 for 198.
Overnight leader Graeme McDowell of Northern Ireland recovered from a double-bogey, bogey opening to squeeze out a one-under 70 that left him tied for third on 200.
He was joined in that group by Scotland's Russell Knox -- fresh off his victory in the WGC HSBC Champions in Shanghai -- who posted his second successive 65.
American Justin Leonard (67) and Harold Varner (68) rounded out the group on 13-under, with American Johnson Wagner a further shot back on 201.
"I was just out there having fun, trying to make jokes with my caddie and keep the mood light and just play golf," the 29-year-old Fathauer said after a round that included four birdies in his first nine holes, and one coming in.
He said he'd try to maintain the same attitude on Sunday and not worry about what his rivals might be doing on a course where low rounds are certainly possible.
"I've just got to go have fun, play golf, play my game," he said.
Bohn, 42, had a share of the lead until a bogey at the final hole, where his approach ran through the green and his putt to save par lipped out.
The two-time winner on the PGA Tour had four birdies in his first nine holes and added a birdie at 12 and an eagle at the 13th before a 90-minute delay for lightning in the area.
McDowell, the 2010 US Open champion trying to find his way back to the winner's circle for the first time since 2013, found himself in trouble at El Camaleon's first hole for the third straight day.
He recovered with birdie braces at five and six and 10 and 11 and after a bogey at 13 a birdie at 17 kept him in the hunt.
"The takeaway is the game's in really good shape," McDowell said. "Apart from two driver swings today, I was really happy with the general progress."