American golfer Charley Hoffman leads the Texas Open by one stroke after carding a bogey-free five-under-par 68 in San Antonio on Thursday.
Hoffman - a three-time PGA Tour winner - did not drop a shot throughout his opening 18 holes at the TPC San Antonio, holing five birdies for sole possession of top spot.
The 38-year-old was three-under 33 at the turn courtesy of three birdies and he added another two on the back nine, including the penultimate 17th hole.
Australian Aaron Baddeley is a shot off the pace after an eventful day on course.
After hooking his ball well left of the green on the short par-four 17th hole, Baddeley decided to take an unplayable and re-tee his ball to hit his third shot.
Not only did the 34-year-old hit this one straight, he knocked it straight in the hole.
Even though he managed a birdie after the amazing shot, Baddeley could have walked away with a rare albatross, via a hole-in-one, on a par-four.
Andrew Magee remains the only player to ever record a par-four ace in PGA Tour history, doing so on the par-four 17th at TPC Scottsdale in the 2001.
American Max Homa is a shot further back, while countrymen Phil Mickelson and Ryan Palmer are tied for fourth spot at two under.
A group of seven Americans are level at one under after round one - Cameron Beckman, Daniel Summerhays, Jordan Spieth, Jimmy Walker, Chris Kirk, Zach Johnson and Chesson Hadley.
Meanwhile, 2010 US Open champion Graeme McDowell withdrew after just nine holes due to an ankle injury with The Masters looming.
"Apologies to everyone at @valerotexasopen for my withdrawal," McDowell tweeted afterwards. "Strained my lower left leg/ankle area practicing y/day and played with heavy strapping on it in the pro am and this morning.
"With The Masters upcoming I decided that getting fit is imperative. Don't like WDs [withdrawals].
"The week here at @valerotexasopen had everything I wanted. Great people and great course. Disappointed this has happened. Thanks to everyone."
Bae Sang-Moon (back) and Colt Knost (wrist) also withdrew.