Dustin Johnson turned in 33 to edge into a one shot lead on day two of the WGC-Mexico Championship at Chapultepec Golf Club.
The American is the only player to have won all four World Golf Championships events and has claimed this one twice, including its first staging in Mexico City two years ago.
The Saudi International powered by SBIA champion began the day a shot behind overnight leader Rory McIlroy and at one point trailed the Northern Irishman by four, but two birdies on the front nine were enough to move him ahead at nine under.
McIlroy was one shot behind alongside American Matt Kuchar, with Spaniard Sergio Garcia, England's Tommy Fleetwood and Australian Cameron Smith at six under.
McIlroy eagled the par four first after driving the green on day one and he was through the putting surface in round two but got up and down from a bunker.
A booming drive on the second allowed him to make the putting surface again and two putts meant he was the first man this week into double figures.
Another huge drive helped set up a chance from five feet on the fourth and McIlroy led by four but Kuchar and Johnson were on the move.
Kuchar got up and down from the side of the first, put an approach to ten feet on the second and then his tee-shot to four feet on the third to get to eight under.
Johnson joined him with a 14-footer at the fourth but the 40-year-old put an approach to nine feet to start with four birdies and get within two.
McIlroy then found the water with his second at the par five sixth and after having to correct his drop after initially dropping from shoulder height, surrendered a bogey.
Johnson took advantage of the same hole to cut the lead to one and Kuchar three-putted the sixth for a first bogey of the day.
McIlroy had found the fringe with his second shot on the ninth but he four-putted for a double-bogey and Johnson was all of a sudden in the lead.
Garcia drove the green on the par four first and got down in two, holed a 13-footer on the second and put his tee-shot on the par three third to five feet for a birdie-birdie-birdie start.
The 39-year-old then took advantage of the par five sixth and 11th but could not get up and down from a bunker on the 14th.
Fleetwood made a spectacular start, driving the first green and pitching in at the second to become the first player in ten years to begin his round eagle-eagle on the European Tour. A 21-foot putt on the eighth then had him within three of the lead.
Australian PGA Championship winner Smith birdied the 12th and 14th and then recovered from a bogey on the 17th with further gains on the first, fourth and sixth.
Richard Sterne was at five under, a shot clear of Kiradech Aphibarnrat, Tyrrell Hatton, Charles Howell III, Ian Poulter and Tiger Woods.
