Brian Davis claimed a one-shot lead after two rounds of the Honda Classic in Palm Beach Gardens, Florida but it could have been much better for the Londoner.
Davis, who had a bogey-free opening round, carded birdies at the 12th, 13th and par-five 18th after starting on the back nine at the PGA National course.
He followed that with two birdies through his next four holes, before undoing much of his good work with a double bogey at the seventh and a bogey at the ninth.
His three-under-par 67 put him eight under on 132 overall and one shot ahead of Matt Jones, who also carded a 67 and was two ahead of Dudley Hart - the 2000 winner of this event.
John Mallinger and Ben Crane were tied for fourth - three shots back - and Ernie Els, the world's fourth-ranked player, was bunched with five others at three-under 137.
Davis, who is aiming for his first PGA Tour win, said: "Around this course, I think you'd need about a 20-shot lead with one round to go.
"You know around here, it's going to come down to the last nine holes, just the way the course is set up. I can't see anybody getting a six-shot lead out there tomorrow.
"I'm sure every player's got a few hiccups around here. But it's a welcome return to form and it's where you want to be."
Australian Jones had birdies on three of his first five holes, before a bogey on the 11th left him two shots under. However, the 27-year-old carded his 10th birdie of the tournament on the next hole to help finish his day in second place.
The 39-year-old Hart carded six straight birdies on the front side to move to six under, but a double-bogey at the par-three 17th kept him from finishing the day with a share of the lead.
"You don't birdie six in a row very often," said Hart.
"You know, everybody out here has gone through stretches where they have done that. It's just hard to describe, really - just things are clicking right. The putts are falling, and good things are happening."
First-round leader Luke Donald shot a four-over 74, including a quadruple-bogey on the 14th to fall six shots back.
Defending champion Mark Wilson shot a three-over-par 73 for the second consecutive day and missed the cut.
