Sean Crocker maintained his narrow one-shot lead after following up Thursday's 63 with a flawless 66 on day two of the 2022 Hero Open.
On another day of impressive scoring at Fairmont St Andrews, Crocker made the most of favourable morning conditions to fire six birdies - three on each side of the course - and get to 15 under par.
And although the course record he had set in the first round was broken by both his playing partner Ewen Ferguson and afternoon starter Wilco Nienaber, who produced bogey-free 61s on Friday, no-one was able to catch Crocker at the summit.
Home favourite Scott Jamieson was alone in second on 14 under, one stroke ahead of Jonathan Thomson, Jens Dantorp, David Law, Adrian Otaegui and later starter Ross Fisher.
Starting from the tenth tee, Crocker birdied the 11th from 16 feet following a fine tee-shot at the par three.
He notched his second birdie of the day at the 15th before picking up another shot on the 18th from five feet.
The American made it back-to-back birdies from around 13 feet on the first green before narrowly missing his lengthy effort at the next.
A close-range birdie followed at the par-five third and Crocker completed his second round with a brilliant birdie from 14 feet on the ninth to lead the tournament at the halfway stage.
Crocker, who is aiming to secure his maiden DP World Tour title, said: "It’s always tough to come back out the next day after playing really well.
"It was a little bit calming and nice to get out there, get off to a decent start, and just keep plodding along through the golf course.
"Nothing crazy (has clicked on the greens this week). I enjoy the greens. Me and Stevie (caddie Steve Pettit) are working well together, we’re just getting up, picking a line, and not thinking more. Just stroking it down the hole and hoping it goes in.
"I just want to have some fun, have some laughs on the golf course, hit good golf shots and see what the total adds up to at the end of the week."
Jamieson reached the halfway mark without carding a single bogey thanks to Friday's 64, which contained eight birdies.
He said: "There’s a long way to go. The tournament doesn’t begin until the back nine on Sunday and that’s when your game plan will change, depending on your position in the tournament."