Derek Fathauer carded a five-under-par 66 on day three of the OHL Classic at Mayakoba to take a one-stroke lead into the final round.
The 29-year-old managed six birdies in another bogey-free round to finish the Saturday session on 16-under for the tournament, one clear of Jason Bohn, who shot 65.
Overnight leader Graeme McDowell failed to build on his dazzling second-round of 63, with a double-bogey at the first setting the tone for a modest round of 70 for the Northern Irishman.
McDowell finished the day as one of four players on 13-under, along with Scotland's Russell Knox, Justin Leonard and Harold Varner III, who also endured contrasting fortunes after following up his 62 on Friday with a 68.
Elsewhere, Sweden's Freddie Jacobson catapulted himself into contention courtesy of a third-round 63 as he sits five shots back on 11-under, level with five other players.
