Jordan Spieth had a bogey-free first day to sit two strokes ahead of the field with Sergio Garcia on seven-under 63 at the Charles Schwab Challenge in Fort Worth, Texas.
The Texan, who won at Colonial Country Club in 2016, putted strongly to gain more than four strokes on the greens and missed just one putt from 18 faced inside 20 feet.
Spain’s Garcia, who snared his first PGA Tour victory at Colonial 20 years ago, had a trio of birdies from the eight to the 10th holes before he eagled from a bunker on the par-five 11th.
Americans Erik Compton and Jason Kokrak each carded 65 while their compatriots Brandt Snedeker and Kramer Hickok were another stroke back with Canadian Adam Hadwin.
Newly-crowned US PGA champion Phil Mickelson had a poor start in his attempt to push for an unlikely Ryder Cup place, with the 50-year-old recording a 73 after five bogeys to sit 10 strokes back along with Scotland's Russell Knox.
Ireland’s Graeme McDowell carded a 74 for a share of 98th.
Collated first round scores (USA unless stated, Par 70):
63 Sergio Garcia (Spa), Jordan Spieth
65 Erik Compton, Jason Kokrak
66 Adam Hadwin (Can), Kramer Hickok, Brandt Snedeker
67 Byeong-Hun An (Kor), Talor Gooch, Patton Kizzire, Sebastian Munoz (Col), Robert Streb, Cameron Tringale
68 Daniel Berger, Doug Ghim, Troy Merritt, Ian Poulter (Eng), Doc Redman, Patrick Reed, Justin Rose (Eng), Sepp Straka (Aut), Brian Stuard, Richy Werenski
69 John Augenstein, Joseph Bramlett, Tony Finau, Brian Harman, J. J. Henry, Kevin Kisner, Tyler McCumber, Collin Morikawa, Joaquin Niemann (Chi), Henrik Norlander (Swe), Andrew Putnam, Rory Sabbatini (Svk), Kyle Stanley, Kevin Streelman, Camilo Villegas (Col), Vincent Whaley, Will Zalatoris
70 Abraham Ancer (Mex), Wyndham Clark, Corey Conners (Can), Cameron Davis (Aus), Brice Garnett, Emiliano Grillo (Arg), Harry Higgs, Nate Lashley, Adam Long, Maverick McNealy, Carlos Ortiz (Mex), Pat Perez, Scottie Scheffler, Robby Shelton, Peter Uihlein, Gary Woodland
71 Scott Brown, Charley Hoffman, Billy Horschel, Sung Jae Im (Kor), Matt Jones (Aus), Chris Kirk, Andrew Landry, Chengtsung Pan (Tai), Hudson Swafford, Nick Taylor (Can), Matt Wallace (Eng), Xinjun Zhang (Chn)
72 Jason Dufner, Dylan Frittelli (Rsa), James Hahn, Mackenzie Hughes (Can), Zach Johnson, Si Woo Kim (Kor), Danny Lee (Nzl), Cameron Percy (Aus), Scott Piercy, Patrick Rodgers, Sam Ryder, Chase Seiffert, Scott Stallings, Henrik Stenson (Swe), Justin Thomas, Michael Thompson, Brendon Todd, Jimmy Walker
73 Rafael Cabrera (Spa), Brian Gay, Russell Knox (Sco), Denny McCarthy, Phil Mickelson, Keith Mitchell, Kevin Na, Matthew NeSmith, Adam Schenk, Sahith Theegala, Jhonattan Vegas (Ven)
74 Joel Dahmen, Lucas Glover, Mark Hubbard, Sung-Hoon Kang (Kor), Matt Kuchar, Luke List, Peter Malnati, Graeme McDowell (Irl), Ryan Palmer, D. A. Points, J. T. Poston, Harold Varner III
75 Cameron Champ, Austin Cook, Will Gordon, Tom Hoge, Lee Westwood (Eng), Tom Lewis (Eng)
76 Branden Grace (Rsa)
77 Michael Gligic (Can), Brandon Hagy, Anirban Lahiri (Ind), Michael Visacki
80 Keith Clearwater