Sebastian Munoz became the first player in PGA Tour history to card two rounds of 60 in the same season after dominating the first day of the AT&T Byron Nelson.
The Colombian, who also recorded an opening 60 at the RSM Classic at Seaside in Georgia in November, will head into the second day four shots clear after an impressive 12-under par round in Texas.
Munoz made eagles at the ninth and 12th with four birdies over the last five to complete a course record on Thursday.
“It’s a great feeling when everything is clicking,” said the 29-year-old.
“When you are hitting the tee shots, the ball is coming out in the window that you imagined, and you’re reading good the putts.
“When everything is going, it’s just stay out of the way and just kind of let it happen.”
Defending champion Lee Kyoung-hoon, Mito Pereira, Peter Malnati and Justin Lower are in a tie for second place after carding eight-under 64s.
Ireland’s Seamus Power and Englishman David Skinns are on six under.
World No 1 Scottie Scheffler and three-time major winner Jordan Spieth both carded 67s, with English duo Ian Poulter and Luke Donald nine shots off the pace.
