Charles Howell III shot an eight-under-par 63 to hold a share of the first-round lead alongside Ollie Schniederjans at the John Deere Classic in Illinois.
American Howell is looking to win his first US PGA Tour title for 10 years, but has been in good form this season with a couple of runner-up finishes to his name.
The 35-year-old made eight birdies in a flawless round, the highlight of which was a 25-feet effort on the seventh.
Schniederjans, who finished 12th at the Open in 2015 as an amateur, had nine birdies but dropped a shot on the 18th after his approach came up short of the green.
Two-time major winner Zach Johnson, fellow Americans Patrick Rodgers and Chad Campbell and South Africa's Rory Sabbatini share third on six under.
England's Sam Horsfield, who came through qualifying to take his place in the field, is the leading European after a five-under 66 left him tied for seventh, while Ireland’s Seamus Power is tied for 55th place on one under.
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