Dallas - James Hahn fired a bogey free six-under 64 to take a share of the lead with fellow American Ricky Barnes after the first round of the PGA Tour's Byron Nelson tournament on Thursday.
Hahn, who is seeking his third win on the Tour, tallied six birdies with no bogeys at the Four Seasons Resort course.
Matt Kuchar, Jhonattan Vegas of Venezuela, Jason Kokrak and Cameron Tringale are two strokes back after carding 66s.
World number one Dustin Johnson, Bud Cauley, Brooks Koepka, John Huh, Sean O'Hair, Ryan Armour and Peter Malnati were tied for seventh after shooting 67s.
Scores in the afternoon averaged more than two strokes higher than the morning group, as winds swirled around the Texas course.
Hahn, whose last win was at the 2016 Wells Fargo Championship, found the fairway on 12 of 14 chances and hit all but one green in regulation.
"It's playing tough out there," Hahn said. "You know, once you start counting up your strokes in the middle of the round it's kind of when things go haywire.
"I had a great conversation with my caddy on almost every hole trying to leave ourselves the best opportunity for a birdie."
Barnes, the 2002 US Amateur champion, went on an up-and-down ride, as his scorecard featured eight birdies and two bogeys.
"I played solid, kept the hole in front of me even though I didn't hit many fairways," Barnes said.
Johnson two-putted from 90 feet on the 18th hole to stay a part of his group.
"I felt like I hit a lot of good shots and ended up in really bad spots due to the wind conditions blowing really hard and it's gusty, which made it tough," Johnson said.
"It was tough to judge the distance, tough putting, tough all around."
World No 6 Jordan Spieth and fourth-ranked Jason Day of Australia headlined a list of 12 players at 68.
Leading scores after the first round of the PGA Tour's Byron Nelson tournament (USA unless noted):
64 - James Hahn, Ricky Barnes
66 - Matt Kuchar, Jhonattan Vegas (VEN), Jason Kokrak, Cameron Tringale
67 - Bud Cauley, Brooks Koepka, John Huh, Sean O'Hair, Dustin Johnson, Peter Malnati, Ryan Armour