A fast finish saw Graeme McDowell card an eight-under 63 to take a one-shot lead at the OHL Classic at Mayakoba on Friday.
The Northern Irishman holed nine birdies at the El Camaleon Golf Club in his second round to move into 12 under and go top of the leaderboard.
McDowell produced eight of those in the space of 10 holes in Playa del Carmen, Mexico.
The 2010 U.S. Open champion finished the day a shot clear of Derek Fathauer (66), the American who is one stroke ahead of Kim Si-woo (64) and Harold Varner III (62).
"I went through a spell in my career where winning started to become a little easier," McDowell said as he eyes his first PGA Tour win since 2013.
"I've had a spell here the last 18 months where making cuts has been hard and getting in contention has been difficult.
"I feel like I've got enough resources to pull on going into a weekend like this one. The keys are not getting too far ahead of myself and staying in the present. This is not the last-chance saloon this weekend."
Varner produced a brilliant round to surge into contention on the back of 10 birdies and just the one bogey.
A group of five Americans are tied for fifth in Patrick Rodgers (66), Jason Bohn (63), Justin Leonard (68), Shawn Stefani (68) and Brice Garnett (66).
Stefani was runner-up at the event last year and could be even better placed if not for a double-bogey at the par-four 14th.
Johnson Wagner (67), Scott Brown (67), Spencer Levin (66) and Michael Thompson (68) are at eight under, in a tie for 10th.
Defending champion Charley Hoffman was among those missing the cut as his 70 left him at one under and a shot adrift of making it to the weekend.