Dustin Johnson opened up a two shot lead heading into the weekend at the WGC-Mexico Championship but he had a host of European Tour stars chasing him down at Chapultepec Golf Club.
The American stretched his bogey-free run in Mexico City to 48 holes with a 67 that moved him to 11 under, with fellow American Matt Kuchar and four time Major Championship winner Rory McIlroy his nearest challengers.
England's Tommy Fleetwood carded a 65 to sit at seven under alongside Spaniard Sergio Garcia, one shot clear of England's Ian Poulter and Australian Cameron Smith.
Saudi International powered by SBIA champion Johnson is the only player to have won all four World Golf Championships titles and has claimed this one twice, including its first staging in Mexico City two years ago.
"I just hit a lot of fairways, hit a lot of greens," he said. "My speed has been pretty good with the putter. I feel like I'm swinging really well, I've got a lot of confidence in the game so I'm looking forward to this weekend."
McIlroy got up and down from a bunker for a birdie on the first and another booming drive on the par four second allowed him to make the putting surface, with two putts making him the first man this week into double figures.
A 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.
Kuchar joined the lead from five feet on the ninth but Johnson edged back ahead with an 11-foot left-to-righter on the tenth.
The two were going toe-to-toe and Kuchar made the most of the par five 11th but Johnson holed from 11 feet again on the 12th before McIlroy played a stunning approach to the 14th. Kuchar then three-putted the 16th to leave Johnson two clear.
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 helped him turn in 30 and he capitalised on the par fives on the back before surrendering a three-putt on the 17th.
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. He bounced back on the par five next and hit an excellent approach into the 16th but bogeyed the last after hitting a tree off the tee.
Australian PGA Championship winner Cameron Smith carded a 67, with Poulter recording a 68.
Tiger Woods carded a 66 with six birdies and a bogey to get to five under but his round will be remembered for his second shot on the ninth. The 14 time Major Championship winner was in a bunker and blocked out but hit an outrageous slice around the trees and saw his ball hop right and finish 11 feet from the hole.
Kiradech Aphibarnrat, Tyrrell Hatton, Charles Howell III and Richard Sterne were also six shots off the lead.