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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.
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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)
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