American pair James Hahn and Ricky Barnes upstaged a star-studded field to take the lead after the opening round of the AT&T Byron Nelson.
World number one Dustin Johnson, Masters winner and defending champion Sergio Garcia, Jordan Spieth and Jason Day are all competing in Texas this week but it was Hahn and Barnes who found themselves atop the leaderboard early.
Hahn and Barnes carded six-under-par 64s for a share of the two-stroke lead on Thursday.
A two-time PGA Tour winner, Hahn – who last claimed the Wells Fargo Championship in May last year – was flawless throughout his opening 18 holes, posting six birdies.
Barnes – still searching for his maiden title – was not bogey-free but he did hole eight birdies, including three in succession from the sixth to the eighth.
Matt Kuchar, Jhonattan Vegas, Jason Kokrak and Cameron Tringale are four under heading into the second round.
U.S. Open champion and golf's top player, Johnson, headlines a group of men three shots off the pace.
Returning from a back injury – which saw him following up his runner-up placing at Wells Fargo with a T12 at the Players Championship – had a first-round 67 thanks to five birdies and two bogeys.
Two-time major champion Spieth is a shot further back, alongside former world number one Day, who holed an eagle, four birdies and as many bogeys in a mixed round.
Garcia's start to his title defence did not go according to plan, with four bogeys ensuring he ended the opening round three over the card.