Gary Woodland carded a six-under 65 to take a one-shot lead after the second round of the OHL Classic at Mayakoba.
The American, who opened with a 64 at the El Camaleon Golf Club, moved into 13 under on Friday.
He is ahead of Webb Simpson (65), who is a shot clear of another American in Scott Piercy (66).
Woodland produced a bogey-free round that included six birdies, three of which came on his final four holes.
Simpson also finished strongly, three straight birdies from the sixth to eighth - on his back nine - seeing him into outright second.
Piercy's only blemish came at the par-three 15th, but he remains well placed after a consistent start.
They're... everywhere. https://t.co/JyMGskOc2c-- PGA TOUR (@PGATOUR) November 11, 2016
A group of seven players are tied for fourth at nine under.
Chris Kirk, the overnight leader, is among them after producing a one-under 70 in his second round.
Ben Martin (64), John Huh (66), Abraham Ancer (68), Adam Hadwin (66), Russell Knox (65) and Charles Howell III (64) are also at nine under.
Graeme McDowell, last year's champion, just survived the cut, moving into two under with a 65.
Ian Poulter, Ernie Els, Jim Furyk and Luke Donald were among those failing to make it to the weekend.