Peter Hanson recorded a round of 65 on the opening day of the Byron Nelson Championship to take the lead in Irving.
The Swede, who had issues with a back problem prior to the start of the competition, benefited from a strong display on his front nine as he went out in just 30 shots.
Hanson was unable to take the momentum into the second half of his round as he failed to pick up any further strokes before settling for five-under-par.
Three players are tied for second place behind Hanson, with Marc Leishman, Tim Wilkinson and David Duval just one shot worse off than the leader.
Former world number one Duval, who is currently ranked 890th in the world, took full advantage of a rare appearance on the PGA Tour as he recorded three birdies in his final three holes to climb up the leaderboard.
Players Championship winner Martin Kaymer is among a group of eight competitors in the hunt on three-under after the first round.
