American Scott Langley failed to take full advantage of four birdies in his first seven holes but despite a mixed bag after the turn he crept to the top of the leaderboard in the Travelers Championship in Connecticut.
The Illinois golfer began the day just a stroke off the lead and got his second round, starting at the 10th, off to a flyer with that run of birdies to reach the turn in 31.
While the birdies - another four - continued they were interspersed with double bogey and another dropped shot as he posted 65.
His 11-under score kept him just ahead of Michael Putnam, who had an even better first nine with five birdies in seven holes, having begun by bogeying the 10th, and added three coming home to card a 63.
South Korean KJ Choi also made the most of going out off the 10th with four of his six birdies coming before the turn as he carded a second successive 65 to also move into joint second on 10 under with Harris English joining him after a 64.
Overnight leader Brendan Steele shot a 69 to sit two shots off the pace.
Langley believes he has learned a valuable lesson from three weeks ago when he was in the final pairing for the last round of the Memorial Tournament but shot 79.
"When I get in those situations I need to keep my head down and just play golf," he said.
"I probably didn't handle it as well as I could have but I learned from it, and going into this weekend, I'm not going to talk about what it would mean to win.
"I'm just going to keep my head down and keep playing golf, just stay in my own little world and play the game because I've done it pretty well the last two days."