SILVIS, 10 Jul 2015 (AFP) - Thomas, who contended at last week's Greenbrier Classic and is gunning for his first US tour title, began on the back nine and rolled in 10 birdies in his round.
Thomas, who had an early start, had three straight pars from 10.
He drained a six-footer for birdie at 13, but gave that shot back with a bogey on 14.
He responded by going on a run to finish up his front nine. Thomas ran off four straight birdies from 15, capped off by a putt from 53 feet at the par-four 18th.
A pair of pars at one and two started off Thomas' closing nine. Thomas, 22, finished up with a par at the ninth.
"It's hard not to shoot really low when you make that many putts today. It was great to see them falling," said Thomas. "I hit some bad shots, but when I hit them bad I seemed to leave them in the right spots. It was a really good day, it was fun."
Thompson, playing in the afternoon, also started on the back nine.
"You know, I played well, hit a lot of good golf shots. Most importantly, I hit a lot of fairways," Thompson said. "I had a group with two good guys in it and we all played pretty good, made a lot of birdies. I think everybody fed off each other."
Luke Guthrie bogeyed the last hole and he fell into a share of third place with Charles Howell. They shot seven-under 64s.
American Steve Stricker, who has won this event three times, is in the hunt once again following his six-under 65. He is tied for fifth with Robert Garrigus, Daniel Summerhays, Shawn Stefani and Steven Alker.
Defending champion Brian Harman shot a four-under 67, putting him in a tie for 21st.
Leading first-round scores on Thursday in the PGA Tour's $4.7 million John Deere Classic (USA unless noted, par-71):
63 - Nicholas Thompson, Justin Thomas
64 - Charles Howell, Luke Guthrie
65 - Steve Stricker, Robert Garrigus, Steven Alker (NZL), Daniel Summerhays, Shawn Stefani
66 - Boo Weekley, Carl Pettersson (SWE), Tom Gillis, Zach Johnson, Spencer Levin, Tyrone Van Aswegen (RSA), Brian Stuard, Michael Thompson, Will Wilcox, Robert Streb, Scott Pinckney
67 - Glen Day, Vijay Singh (FIJ), Alex Cejka (GER), Jhonattan Vegas (VEN), Scott Piercy, Brian Harman, Jonas Blixt (SWE), Byron Smith, Steve Wheatcroft, Martin Flores, Sam Saunders, Tony Finau, Kyle Stanley, Jim Renner, Patrick Rodgers, Lee McCoy