America's Sean Crocker carded a course-record 63 to top the leaderboard after a day of remarkably low scoring in the Hero Open.
Crocker recorded an eagle and eight birdies at Fairmont St Andrews to finish nine under par, a shot ahead of a five-strong group which included England’s Ashley Chesters and Ben Stow, the world number 1,719.
Six players were a shot further back on seven under as 119 of the 156-man field took advantage of calm conditions to break par.
Crocker is seeking a first title on the DP World Tour and admitted a string of nine missed cuts in succession earlier this season had forced him to "grow up".
"Mentally that was probably the toughest thing I’ve gone through so far," the 25-year-old said.
"I know a lot of people have spoken about the whole mental side of sport but that was probably the darkest I’ve been in my whole life on a golf course.
"It was the first time I’ve experienced bad things happening on a golf course and I pretty much just had to grow up.
"I had to look at it and go well 'OK, you’ve been lucky enough to play good golf pretty much your whole life so far and now you’re going to get a little taste of what this game is all about'.
"It made me aware of just how hard this game is and also realise I can do all the work and still hit bad shots – there’s no point in getting upset."
Niall Kearney is best of the Irish after a round of 68, with defending champion Grant Forrest and Cazoo Classic winner Richie Ramsay also five shots off the lead.
