Charley Hoffman fired an eight-under 64 to take a one-shot lead at the Houston Open on Thursday.
The American holed nine birdies at the Golf Club of Houston to take the lead on a good day for scoring.
Dustin Johnson shot a 65 to make a good start, while world number two Jordan Spieth carded a fine five-under 67.
However, Hoffman leads after his fine round, which started with four birdies on his first five holes before his only blemish of the day - at the 16th.
He produced four-straight birdies from the first hole to the fourth to start his front nine before another at the eighth put him in control.
Johnson had a mixed round, producing an eagle with seven birdies and two bogeys.
The American is joined in a tie for second by Roberto Castro, Scott Brown and Morgan Hoffmann.
Johnson Wagner, Justin Hicks, Chez Reavie and Scott Pinckney all produced 66s to be tied for sixth on a congested leaderboard.
Steve Marino, fresh from his runner-up finish at the Puerto Rico Open, is alongside Spieth at five under.
They are joined by nine others, including Swede Jonas Blixt and Canadian Graham DeLaet.
Spieth, eager to build some momentum ahead of The Masters, started well with four birdies on the front nine.
A bogey at the 10th slowed him down before back-to-back birdies at 14 and 15 saw him finish well.