Jim Herman fired a 7-under 64 on Thursday to grab a 2-stroke lead at the Nationwide Children's Hospital Championship before play was suspended for darkness.
There was a three-plus hour rain delay earlier in the first round, causing the eventual suspension.
Sean O'Hair and Danny Lee carded matching 5-under 66s at Ohio State University Golf Club's Scarlet Course to grab a share of second place, while Miguel Angel Carballo and Andrew Putnam shot 4-under 67s to tie for fourth.
Andrew Svoboda, Ben Kohles and Tim Petrovic also sat at 4-under, but will have to complete their first rounds on Friday morning. Svoboda was through 16 holes of his first round, while Kohles and Petrovic both completed 15.
Herman opened his round with a birdie at the first, and later snapped a streak of four straight pars with consecutive birdies at the sixth and seventh to make the turn at 3-under.
He picked up another shot with a gain at the 10th. Herman closed his round with three birdies over his final four holes, including a tap-in birdie at the last after nearly holing out for an eagle, to move into first at 7-under.
"We won the high school state championship here. State champs with St. Xavier High School," said Herman, who grew up in Cincinnati. "I wasn't the individual champ but our team was victorious. That was back in the fall of '95. Always good memories here."
O'Hair started his day with three straight pars before getting on the board with an eagle at the fourth. He then countered a birdie at the sixth with a bogey at the seventh to remain at 2-under.
A birdie at the 12th moved him to minus-3, and he poured in back-to-back birdies at the 16th and 17th to own the clubhouse lead at 5-under before Herman's late push moved him ahead.
Lee went out with the later group and countered a lone bogey with six birdies to meet O'Hair in second place just moments before play was halted for the day.
NOTES: Thirty players will need to complete their first round when play resumes at 7:45 a.m. ET Friday ... Friday's second round is scheduled to start at 8:40 a.m. ... Herman made the cut in 10 of 19 starts on the PGA Tour this year, including a pair of top-10 finishes.