Roberto Castro has taken a two-shot lead at the AT&T National after he recorded a five-under-par first round of 66.
The American began his round with a bogey at his second hole, but he responded with six birdies to lead a group of three players.
Billy Horschel, who has enjoyed a superb first season on the PGA Tour, is one of the closest challengers to Castro, and he is joined on three-under by Bud Cauley and Graham DeLaet.
Jim Furyk, Nicolas Colsaerts and Brandt Snedeker are part of a group of players on two-under, while Brian Davis leads the English challenge on one-under.
