Ireland's Seamus Power was three shots off the pace after carding a four-under 66 on the opening day of the Travelers Championship.
Satoshi Kodaira of Japan and Kramer Hickok – seeking a breakthrough win on the circuit – each scored a 63 at TPC River Highlands in Connecticut to be seven-under and one stroke ahead of Hickok’s fellow American Talor Gooch.
Power, 34, mixed six birdies with a pair of bogeys for his 66, while Englishman Tom Lewis carded a 67 after he recovered from double-bogeying the par-four fourth hole with five birdies in his remaining play.
Lewis’s compatriot Ian Poulter was five shots back from the leaders on two-under 68, with Justin Rose joining defending champion Dustin Johnson in carding an even-par 70.
England’s Paul Casey struggled to overcome a horror start in which he bogeyed his first four holes from the 10th to the 13th en route to scoring a one-over 71.
Scotland's Russell Knox, meanwhile, was 10 strokes off the pace at three-over 73 while Luke Donald had six bogeys and a double-bogey on a horror day which ended with him 15 shots behind Kodaira and Hickok.
Following a round of eight birdies and a bogey, Hickok said: “I got off to like the worst warm-up session of the year this morning and was just hitting it everywhere, and so I really changed my strategy. I was just trying to play a little bit more conservative, hit greens, and once the putts started to fall, I just knew it really freed me up.”
Collated first round scores (USA unless stated, Par 70)
63 Kramer Hickok, Satoshi Kodaira (Jpn)
64 Talor Gooch
65 Brice Garnett, Beau Hossler, Maverick McNealy, Henrik Norlander (Swe), Patrick Rodgers
66 Sam Burns, Zach Johnson, Kevin Stadler, Sepp Straka (Aut), Bubba Watson, Seamus Power (Irl)
67 Joseph Bramlett, Harris English, Russell Henley, Tom Hoge, Mackenzie Hughes (Can), Tom Lewis (Eng), Sebastian Munoz (Col), Ted Potter Jr., Cameron Smith (Aus), Kevin Streelman
68 Byeong-Hun An (Kor), Jonas Blixt (Swe), Patrick Cantlay, Kevin Chappell, Stewart Cink, Doug Ghim, Michael Gligic (Can), Brian Harman, Jim Herman, Sung-Hoon Kang (Kor), Peter Malnati, Troy Merritt, Joaquin Niemann (Chi), John Pak, Pat Perez, Ian Poulter (Eng), Brandt Snedeker, Robert Streb, Brendon Todd, Stephen Stallings Jr.
69 Scott Brown, Jason Day (Aus), Bryson DeChambeau, Tyler Duncan, Rickie Fowler, Scott Harrington, Garrick Higgo (Rsa), Max Homa, Mark Hubbard, Brooks Koepka, Chase Koepka, Nate Lashley, Hank Lebioda, Kyoung-Hoon Lee (Kor), Marc Leishman (Aus), Hunter Mahan, Tyler McCumber, Phil Mickelson, Kevin Na, Scott Piercy, Doc Redman, Patrick Reed, Sam Ryder, Scottie Scheffler, Adam Scott (Aus), Brendan Steele, Brian Stuard, Kristoffer Ventura (Nor), Vincent Whaley, Guido Migliozzi (Ita), Andrew Svoboda
70 Ryan Armour, David Hearn (Can), J. B. Holmes, Dustin Johnson, Matt Jones (Aus), Kevin Kisner, Patton Kizzire, Anirban Lahiri (Ind), Sean O’Hair, Carlos Ortiz (Mex), Cameron Percy (Aus), Andrew Putnam, Chez Reavie, Justin Rose (Eng), Kyle Stanley, Nick Taylor (Can), Vaughn Taylor, Kevin Tway, Harold Varner III, Lucas Herbert (Aus)
71 Paul Casey (Eng), Wyndham Clark, Will Gordon, Lanto Griffin, Adam Hadwin (Can), J. J. Henry, Chris Kirk, Danny Lee (Nzl), William McGirt, Keith Mitchell, Rob Oppenheim, J. J. Spaun, Cameron Tringale, Richy Werenski
72 Abraham Ancer (Mex), Keegan Bradley, Rafael Campos (Pur), Jason Dufner, Austin Eckroat, Brian Gay, Brandon Hagy, Charley Hoffman, Denny McCarthy, Ryan Moore, Chengtsung Pan (Tai), Adam Schenk, Scott Stallings, Michael Thompson, Sebastian Cappelen (Den), Rafael Cabrera (Spa)
73 Alex Beach, Bronson Burgoon, Harry Higgs, Russell Knox (Sco), Francesco Molinari (Ita), Rory Sabbatini (Svk), Chase Seiffert, Robby Shelton, Roger Sloan (Can), Davis Thompson, Aaron Wise, Grayson Murray, Ryan Brehm, D. J. Trahan
74 Austin Cook, Dylan Frittelli (Rsa), Emiliano Grillo (Arg), Chesson Hadley, Michael Kim, Si Woo Kim (Kor), Matthew NeSmith, Martin Trainer
75 David Lipsky, Hudson Swafford
76 Tony Finau, Adam Long, Matthew Wolff
77 Bo Van Pelt
78 Luke Donald (Eng), Nick Watney
83 Brian Keiser
