SYLVIS, 10 Jul 2015 (AFP) - Thomas had five birdies against a lone bogey to stand on 12-under 130 for a one-stroke lead over compatriots Tom Gillis and Johnson Wagner at TPC Deere Run. Wagner had the day's low round with a bogey-free 63 that featured eight birdies.
Wagner stumbled on the back nine last week at the Greenbrier Classic and missed a chance for his first PGA title since 2012.
The US trio of Scott Pinckney, Daniel Summerhays and Will Wilcox shared fourth on 132 with the American pack of Bryce Molder, Spencer Levin, Robert Garrigus and Steve Wheatcroft sharing seventh on 133.
New Zealand's Steven Alker and Americans Zach Johnson, Luke Guthrie, Steve Stricker and Brian Stuard shared 11th on 134.
Spieth said he was struggling on the practice range Thursday evening and again before Friday's round.
"I knew I needed to shoot at least 67. I wasn't taking it for granted," Spieth said. "I was still searching. I couldn't find any answers."
They started coming on the back nine after Spieth began his round off the 10th tee.
He birdied 14, the par-3 16th, the 18th and first holes to serve notice he was on a roll, then sank a 10-foot eagle putt at the par-5 second.
Spieth followed with birdies at the fifth and par-3 seventh before taking a bogey at eight.
"It's just repetitions," Spieth said. "I'm getting on-course reps and it's making a difference."
Leading scores after Friday's second round of the US PGA John Deere Classic (USA unless noted, par-71):
130 - Justin Thomas 63-67
131 - Johnson Wagner 68-63, Tom Gillis 66-65
132 - Scott Pinckney 66-66, Daniel Summerhays 65-67, Will Wilcox 66-66
133 - Bryce Molder 68-65, Steve Wheatcroft 67-66, Spencer Levin 66-67, Robert Garrigus 65-68
134 - Brian Stuard 66-68, Luke Guthrie 64-70, Zach Johnson 66-68, Steven Alker (NZL) 65-69, Steve Stricker 65-69
135 - Shawn Stefani 65-70, Nicholas Thompson 63-72, Ryan Moore 70-65, Brian Harman 67-68, Jordan Spieth 71-64, Vijay Singh (FIJ) 67-68
136 - Danny Lee (NZL) 68-68, Gonzalo Fernandez-Castano (ESP) 68-68, Jason Bohn 68-68, Michael Putnam 69-67, Derek Fathauer 71-65, Tyrone van Aswegan (RSA) 66-70, Sam Saunders 67-69, Max Homa 70-66, Mark Hubbard 69-67, Chris Stroud 68-68, Chad Campbell 72-64, Boo Weekley 66-70, Charles Howell 64-72, Robert Streb 66-70, Scott Piercy 67-69, Jonas Blixt (SWE) 67-69, Jim Renner 67-69, Jerry Kelly 70-66, Kevin Kisner 69-67, Cameron Percy (AUS) 68-68