Rory McIlroy equalled the lowest opening round of his European Tour career to lead the way after day one of the WGC-Mexico Championship.
The Northern Irishman fired an eagle and seven birdies at Chapultepec Golf Club en route to his fifth first round of 63 and his lowest starting round on the European Tour since 2014.
That left him at eight under, one shot clear of 2015 and 2017 champion Dustin Johnson and three ahead of two more Americans in Matt Kuchar and Justin Thomas.
South African George Coetzee and Englishman Tyrrell Hatton were then four shots off the lead.
McIlroy has not won on the European Tour since 2016 but has finished second five times since then and was showing the sort of form that has brought him four Major Championships.
"It felt pretty stress-free," he said. "I wouldn't say it was easy. I hit a lot of good golf shots, I left myself a lot of tap-ins for birdies and had a nice eagle on the first hole as well.
"I saw some really good signs last year. I played myself into final groups and had some good chances to win and I think this year is just building upon the good stuff that I was able to do last year."
Saudi International powered by SBIA champion Johnson made a birdie-birdie-birdie start from the tenth to join the early lead, making long putts on the tenth and 12th either side of getting on the green in two at the par five 11th.
McIlroy soon joined the seven way tie in top spot, sandwiching birdies on the 11th and 15th - another par five - with an excellent approach into the 12th.
A tee-shot to three feet on the 17th handed McIlroy the lead on his own but Johnson holed an eight-footer on the same hole to make it a two way tie.
McIlroy then produced a stunning tee-shot on the driveable par four first, brushing the edge of the hole and holing the resulting six-footer to get to six under.
Johnson also drove the first green but needed two putts for birdie before McIlroy put an approach to four feet on the second to lead by two again.
Another big drive meant Johnson got on the second in two but he again needed two putts as he cut the lead to one.
A McIlroy approach to five feet at the fourth edged him two ahead again but Johnson holed a 24-footer on the next and when McIlroy got in trouble in the trees down the left of the sixth, the lead was tied.
The 29-year-old was not done, however, holing a 20-foot putt on the eighth to edge himself back into top spot on his own.
Kuchar had birdies on the 11th, 13th, 15th, first, sixth and seventh before a bogey on the ninth, while Thomas made an eagle and four birdies with a single bogey.
Hatton finished a shot out of a play-off here last season and turned in level par with a birdie and a bogey before coming to life on the back nine.
He holed from 16 feet on the tenth and sandwiched a beautiful tee-shot to tap in range on the par three 13th with up-and-downs from the sand on the 12th and 15th.
Playing partner Coetzee put approaches inside 12 feet to birdie the first and eighth before holing an 18-footer on the ninth to share the lead and turn in 32.
He dropped a shot on the tenth but holed a 40-footer on the 14th and took advantage of the next.
Thai Kiradech Aphibarnrat, Americans Billly Horschel and David Lipsky, and England's Ian Poulter were five shots off the lead.