Ryan Palmer shot a 6-under 64 to take a one-shot lead Thursday in the first round of the HP Byron Nelson Championship.
The native Texan made six birdies in a bogey-free round at TPC at Four Seasons in Irving, Texas.
Marc Leishman and Alex Cejka are tied for second after shooting 5-under 65.
Defending champion Keegan Bradley finished at 3 under, while Jason Day finished with a double bogey to fall to 2-under 68.
Phil Mickelson, playing in the event for the first time since 2007, shot even-par 70.
Matt Kuchar, winner of last week's Players Championship, is one of seven players tied for fourth at 4 under.