Miami - Austin Cook drained a birdie on his final hole to complete an eight-under-par 62 and grab a one-shot lead at the halfway stage of the RSM Classic on Friday.
The 26-year-old PGA Tour rookie held his nerve on the last hole of the day on the par-70 Seaside course to move to 14 under, one clear of Brian Gay, who shot a second round 64 at Sea Island, Georgia.
Cook's 18th hole birdie completed another remarkably consistent round for the rookie, who is one of only two players in the field not to have carded a bogey through 36 holes.
"We've just been able to hit the ball really well," Cook said afterwards. "Speed on the greens has been really good and getting up and down has been great.
"Had a couple of stressful putts, but I've been able to roll them in. Everything's going really well right now."
Three players are tied for third, with Taiwan's Pan Cheng-tsung joining American duo Chris Kirk and Vaughn Taylor on nine under, five adrift of leader Cook.
Pan, playing on Sea Island's Plantation course, carded a seven-under-par 65 on the par-72 layout.
Kirk, who had grabbed the lead with a sizzling 63 on the Plantation course on Thursday, found the going harder on the Seaside layout, settling for a level-par 70. Taylor shot a four-under-par 66.
A group of six players were a further shot back on eight under, including Zimbabwe's Brendon de Jonge and Canada's Ben Silverman.
De Jonge and Silverman both shot 67s on the Seaside Course to stay in contention.
Leading scores after Friday's second round of the US PGA RSM Classic on the par-70 Seaside and par-72 Plantation courses at Sea Island, Georgia (USA unless noted):
128 - Austin Cook 66-62
129 - Brian Gay 65-64
133 - Pan Cheng-tsung (TPE) 68-65, Chris Kirk 63-70, Vaughn Taylor 67-66
134 - Brendon de Jonge (ZIM) 67-67, Brandt Snedeker 67-67, Ben Silverman (CAN) 67-67, Andrew Landry 70-64, Blayne Barber 67-67, Brice Garnett 65-69
135 - Kang Sung (KOR) 66-69, Kelly Kraft 70-65, Josh Teater 68-67, Brian Stuard 67-68, Patton Kizzire 66-69, Kevin Kisner 67-68, Bud Cauley 72-63, Bubba Watson 71-64, Jim Herman 67-68, Webb Simpson 67-68, Joel Dahmen 64-71