Martin Laird has moved to the top of the leaderboard at 11 under after six birdies through his first dozen holes at TPC San Antonio.
That has the Scot one shot clear of overnight leader Billy Horschel, who is just even par on the day but has made several key par putts.
In all, there are five players within three shots of Laird, including Rory McIlroy and Jim Furyk, who are 9 and 8 under, respectively.
McIlroy is 3 under on the day and has three birdies over his last five holes, his only hiccup a bogey on the par-4 10th.
Should Laird go on to win, it would be his third career victory on the PGA TOUR. His last came in 2011 at Bay Hill.