Washington - Mexico's Roberto Diaz birdied four of the first five holes on his way to a nine-under par 62 for a two-stroke lead after Thursday's first round of the PGA Tour's John Deere Classic.
Diaz, ranked 430th in the world, was among the last players on the course at TPC Deere Run but completed a bogey-free round to overtake Americans Adam Long and Russell Henley, who shared second on 64.
The 32-year-old from Veracruz fired the low round of his PGA career, one stroke under his opening round at New Orleans in April.
Diaz seeks his first PGA title. His best finish in a tour event was a share of eighth three weeks ago at the Travelers Championship.
The week's best top-five finisher not already qualified for the British Open will receive a berth in next week's final major tournament of the year at Royal Portrush.
For Diaz, that could mean only his second career major start after he missed the cut in the 2017 US Open.
Diaz opened with back-to-back birdies after dropping his approaches inside six feet, then connected on 20-foot birdie putts at the fourth and fifth holes.
Diaz holed out for eagle from 100 yards at the par-5 10th, then sank 12-foot birdie putts at the 14th and par-3 16th holes to seize the solo led at eight-under.
At the par-5 17th, Diaz stopped his approach inches from the cup for a tap-in birdie and closed with a par.
Long and Henley were two back with Scotland's Martin Laird and Americans Andrew Landry, Vaughn Taylor, Ryan Palmer, Zach Sucher and Ryan Blaum another stroke adrift.
Henley, a back-nine starter, made eight birdies, most after putting his approach inside four feet and the last a 48-footer at the par-3 seventh.
But 200th-ranked Henley, whose best finish this year has been a share of 15th at Phoenix, found the rough on his first two shots at nine, which played as the second-toughest hole of the day, and closed with a bogey to fall level with Long.
"This has been a weird year for me," Henley said. "I haven't felt myself playing golf but I put a lot of work in my game.
"I don't think I've ever lost the belief I can have a nice tournament and a nice round. I'm just trying to keep my head down and keep working hard."
Long, this year's Desert Classic winner, made his lone bogey against eight birdies at 11, but the world number 114 sank his longest birdie putt from 24 feet at the difficult ninth.
Leading scores after Thursday's first round of the PGA Tour's John Deere Classic at TPC Deere Run in Silvis, Illinois (par-71, USA unless noted):
62 - Roberto Diaz (MEX)
64 - Adam Long, Russell Henley
65 - Martin Laird (SCO), Andrew Landry, Vaughn Taylor, Ryan Palmer, Zach Sucher, Ryan Blaum
66 - Denny McCarthy, Austin Cook, Ted Potter, Daniel Berger, Joaquin Niemann (CHI), Cameron Tringale, Dylan Frittelli (RSA), Bill Haas, Brendon Todd, Cameron Davis (AUS)
67 - Nick Taylor (CAN), Ollie Schniederjans, Brandon Harkins, Sam Ryder, Ryan Moore, Matthew Wolff, Lucas Glover, Chad Campbell, John Senden (AUS), Beau Hossler, Adam Schenk, Harold Varner, George McNeill, Brice Garnett, Nate Lashley, Jhonattan Vegas (VEN), Brian Harman, Bud Cauley, Peter Malnati, Andres Romero (ARG), Bae Sang-moon (KOR), Freddie Jacobson (SWE)