Grayson Murray took the early lead with a round of 67 in the first round of the Valero Texas Open.
The American ended day one five-under, putting him one shot ahead of compatriots Chesson Hadley, Billy Horschel, Ryan Moore, Keegan Bradley and Matt Atkins.
The 24-year-old shot three birdies on the front nine of the San Antonio course, only faltering on the par-three seventh hole with a double-bogey.
But Murray rallied to hole four more birdies on the back nine and take the top spot on the leaderboard.
Graeme McDowell sits five shots off the lead after he battled to an opening round of 72, a final hole birdie ensuring he finished the first day on level par.
Seamus Power however struggled on Thursday - and he made three double-bogeys on his way to a four over par round of 76.
Of the five players making up the chasing pack with a round of 68, only Horschel and Moore hit a bogey-free round on the AT&T Oaks Course.
Two-time Valero Texas Open winner Zach Johnson finished on two-under 70 after striking a 12ft eagle putt on the par-five 14th hole and three straight birdies on the last holes.
Sergio Garcia, returning to the tournament for the first time in eight years and after a disappointing title defence at the Masters, carded two-over 74, while Adam Scott, who is aiming to hold on to his position of world number 59 to make the US Open next month, finished on 75 after a failing to make a single birdie.
Valero Texas Open first round (USA unless stated, par 72):
67 Grayson Murray
68 Keegan Bradley , Matt Atkins , Chesson Hadley, Billy Horschel, Ryan Moore
69 Roberto Diaz (Mex), Andrew Landry , Joshua Creel, Jon Curran, Harris English
70 Nick Watney , Brendan Steele , Abraham Ancer (Mex), Zach Johnson, Austin Cook, David Hearn (Can), Keith Mitchell, Brandt Snedeker, Corey Conners(Can)
71 Adam Schenk , Brian Stuard , Benjamin Silverman (Can), Paul McConnell, Ryan Palmer , Beau Hossler, Matt Kuchar, Si Woo Kim(Kor), Aaron Baddeley (Aus), Ollie Schniederjans, Jim Furyk, Sang-moon Bae (Kor), Zecheng Dou(Chn), Jimmy Walker
72 Charley Hoffman , Hudson Swafford , Vaughn Taylor, Matt Jones(Aus), Martin Kaymer(Ger), Cameron Champ, Ethan Tracy, Richy Werenski, Ben Crane , Sean O'Hair, J.J. Spaun, Kevin Tway, Brice Garnett , JT Poston, Luke List, Pat Perez, Graeme McDowell(NIrl), Matt Every, Kevin Chappell, Billy Hurley III , Denny McCarthy, Michael Thompson, Joaquin Niemann (a)(Chi), Rod Pampling (Aus), Ryan Armour, Mackenzie Hughes(Can), Dylan Frittelli (Rsa), Johnson Wagner, Brandon Harkins
73 Andrew Putnam , Kyle Thompson , Geoff Ogilvy (Aus), Steve Wheatcroft, Ben Martin , Steve Marino, Bill Haas, Ernie Els(Rsa), Martin Laird(Sco), Kyung Ju Choi (Kor), Andrew Yun, Zac Blair, Chris Kirk, Retief Goosen (Rsa), Sam Ryder, Fabian Gomez(Arg), Hunter Mahan , Ricky Barnes, J.B. Holmes, Jonathan Byrd , Troy Merritt, Tyler Duncan, Jonathan Randolph
74 Jason Kokrak , Harold Varner III , Brian Gay, Bronson Burgoon, Nicholas Lindheim , Julian Suri, Tom Lovelady, Curtis Reed , Jesse Droemer, Daniel Summerhays, John Senden(Aus), Stewart Cink, Scott Piercy, Kevin Streelman , Trey Mullinax, Joel Dahmen, Sergio Garcia(Spa), Russell Knox (Sco), Troy Matteson, Cameron Tringale
75 Martin Flores , Nate Lashley , Brett Stegmaier, Jamie Lovemark, Cameron Percy(Aus), Peter Uihlein, Talor Gooch, Wesley Bryan , Patrick Rodgers, Dominic Bozzelli, Peter Malnati , Shawn Stefani, Xander Schauffele, Adam Scott(Aus), David Lingmerth (Swe), Conrad Shindler, Tom Hoge, Rob Oppenheim, John Huh
76 Sung Kang (Kor), Martin Piller , John Peterson, Seamus Power(Irl), Danny Lee(Nzl), Shubhankar Sharma (Ind), Stephan Jaeger(Ger), Nick Taylor(Can), Anirban Lahiri(Ind)
77 Kevin Na , Chad Campbell , Scott Brown , Xinjun Zhang (Chn), Greg Chalmers(Aus), Michael Kim
78 Whee Kim (Kor), J.J. Henry , Aaron Wise , Cheng-Tsung Pan (Tpe), Lanto Griffin
79 Chris Stroud , Cody Gribble , Chris Paisley (Eng)
80 Kris Blanks , Robert Garrigus , Tyrone Van Aswegen (Rsa)
81 Jhonattan Vegas (Ve)
82 Derek Fathauer , William McGirt , Rick Lamb
83 Steven Bowditch (Aus)
