Through 36 holes at the World Wide Technologies Championship at Mayakoba, Russell Henley has 16 birdies and zero bogeys to sit three strokes clear of the chasing field at 16 under.
Henley closed his opening round with six birdies on the back-nine to seal a 63, and his second time around El Camaleon Golf Club he evenly split his birdies with four on the front and four on the back.
The 33-year-old American has three PGA Tour victories to his name, but none since the 2017 Shell Houston Open.
Tied for second at 13 under is American duo Sam Ryder and Will Gordon, while compatriot Patton Kizzire is the only player in fourth at 12 under.
Sweden's David Lingmerth is the top international talent, alone in fifth at 11 under, and one further back in a tie for sixth is Harry Higgs, who shot Friday's round-of-the-day with his 62 – including an eagle on the par-four third hole.
Matt Kuchar headlines the group tied for ninth at nine under, while some big names are at eight under, eight strokes off the lead.
Reigning back-to-back champion at this event Viktor Hovland is at that number, and he is joined by Collin Morikawa, Francesco Molinari, Davis Riley and Matthias Schwab.
Last week's winner at the Bermuda Championship, Seamus Power, is at seven under, while world number two Scottie Scheffler is with former Masters champion Danny Willett at six under, and former world number one Jason Day is one stroke inside the cut-line at five under.
The biggest name to miss the cut was world number 14 Tony Finau, who bogeyed the 18th hole to lose his right to play on the weekend.