Los Angeles - An Byeong-hun got a hot start with four straight birdies on Friday to shoot back-to-back 66s for the clubhouse lead at the weather-hit Sanderson Farms Championship.
An led first-round leaders JT Poston and Tom Hoge by two shots with a 12-under 132 total as the second round was suspended because of darkness after storms halted play on Thursday.
Post and Hoge shot second-round 70s and were tied for second with fellow Americans George McNeill (67) and Scottie Scheffler (66).
Australia's Cameron Percy was alone in sixth on nine-under through 11 holes.
"I've been putting a lot better the last couple events, so as long as the putts keep dropping, let's see if I can win this season," said An, who is trying to strengthen his position to make the International Presidents Cup team as a captain's pick.
The second round will resume Saturday morning at The Country Club of Jackson in Jackson, Mississippi. Storms halted play in the first round and organizers had to play catchup on Friday.
South Korea's An has made just one bogey in two rounds. He opened his second round with four straight birdies then added two more on eight and nine for six birdies on the front nine. His only blemish came on the par-five fifth hole after hitting his second shot into the water.
An, who turned 28 on Tuesday, has three worldwide wins, including the European Tour's 2015 BMW PGA Championship, but is seeking his first on the US PGA Tour.
"This is my fourth year on the Tour, and I haven't had a win yet, so a win is definitely on my mind," he said.
Ten years ago, An became the youngest US Amateur champion in history. At age 17, he beat Ben Martin in the final at Southern Hills, breaking a record once held by Tiger Woods.
Poston remains in contention just two adrift of An. He won his first tour title at last month's Wyndham Championship.
Hoge played on and finished the 18th hole after the horn sounded because it meant he could sleep later on Saturday.
"It was so dark that I couldn't see the edge of the hole from four feet," Hoge said.
Hoge was one of the fortunate few in his half of the draw to finish his second round Friday.
Twenty groups will complete their second round Saturday morning.
Seventeen-year-old Akshay Bhatia missed the projected cut by three strokes after shooting rounds of 70-74 in his professional debut.
Leading scores after Friday's completion of the storm-interrupted opening round of the US PGA Sanderson Farms Championship at Jackson, Mississippi (par-72, USA unless noted):
64 - Tom Hoge, J.T. Poston
65 - Robert Streb, Cameron Percy (AUS), Seamus Power (IRL), Harris English, Carlos Ortiz (MEX)
66 - An Byeong-hun (KOR), Scott Stallings
67 - Zac Blair, Emiliano Grillo (ARG), Zach Johnson, Mark Anderson, George McNeill
68 - David Hearn (CAN), Patton Kizzire, Joaquin Niemann (CHI), Cameron Davis (AUS), Adam Long, Alex Cajka (GER), Im Sung-jae (KOR), Cameron Champ, Scottie Scheffler, Michael Gellerman
WD - Matt Jones (AUS) 75